What is causing reduced engine power?

Thank you for the great input! You've given me very helpful information to followup on. I'll get back to you with results based on your help and anything else I may discover.

Thanking you for your help and support here KASEKENNY1. What happened today is that after I had cleaned the throttle body (again), taking resistance measurements from its sensor, and actuating the throttle plate motor with a viable output power supply I re-installed the throttle body assembly on the truck. I then performed the "pedal depression/release slow then fast 3 or more times procedure. Started the truck and let it idle for 3 minutes. Shut it off for a couple minutes. Started the truck again and let it idle for 3 minutes again. Shut it off. Started it again and drove it around the block and it started acting up again with all the icons I mentioned before on the dash with the reduced engine power (limp mode). I pulled it back in the driveway and connected my scanner and it read codes P2135, P0222, and P0220. Really depressing! But now, here is the really weird part. When I restarted the truck so that my wife could park her car behind mine (in our narrow driveway) and drove it around the block for this vehicle re-positioning the truck ran fine; great as a matter fact. So, when I pulled it back into the driveway (with my wife pulling her car up behind my truck) I decide to "rev" it several times. Absolutely no problem occurred with response or even any hint of attempting to go into "limp mode". I shut it back off again and re-started it up again several times with revving the engine many times. No problem now. I re-connected my scanner to see if there were any error codes. The scanner reported that there were no error codes. All seems well now. I will keep checking this situation as this is really strange. I will still perform the checks that you mentioned. I'm wondering if I have an intermittent grounding problem or an open/flaky wire connection. It is good though to know there is help and support for people like us from you guys.

Questions on acronyms and possibly if some are the same thing. Please confirm my guess or correct me on each as follows:
1) DTC = Diagnostic Test Code?
2) TAC = Throttle Actuator Controller?
3) ECM = Engine Control Module?
4) PCM = Powertrain Control Module?

Are there even more controller modules or computers in the vehicle referenced by me (justplainwayne)?
Thanks for your expertise.

Great advice KASEKENNY1. Will do. Also, thank you for correcting the acronyms definitions for me. Really good stuff, really helpful. I'm trying to catch up. BTW, drove the truck a couple times more and all's good so far. It still has the check engine light in the dash display but I suppose it will go out by itself since there are no DTC codes now. Thanks again amigo.

Good call KASEKENNY1! The check engine light went off last night on the way home from McDonald's. I still do not have high confidence in this "fixed situation" yet, but, and this is true, it is wonderful to know there are helpers that really know what they are doing, like you guys. This gives us encouragement to stay the course as DIY'rs out here. I really, really do like my GM Silverado truck and it has been good up to this point.

I need to update this situation. 9-27-2019. 2010 Silverado with 5.3L engine, 58,000 mi, LT, 2 wheel drive, and Crew cab. I have been going through the problem I described coming back and going away for almost two months now. I though it was fixed. It came back at the strangest times, usually when in PARK idling. Yesterday we found the problem. (The truck must have heard I was going to get my oscilloscope out and start examining signals. Ha!) Anyway, I noted that the problem seemed to always come back only after I re- installed the "Vortec" top engine plastic cover on it. Big Clue. So, it was noted that the cover was affecting the harness routed around the top/back of the engine. That was the harness that contained the wires going to the TPS (throttle-body position sensor). The wire that was the TPS sensor 2 signal wire (scanner reported "switch B circuit low voltage DTC - P0220 error) which is a purple wire (wire "F" at the TPS) was routed on the outside level/layer of the harness right up against the transmission dip stick tube (TDST). The TDST vibrates like a "tuning fork", especially at idle in PARK. (In drive it seems to not oscillate like a "tuning fork" so much.) I got up into the engine compartment to look closely at that purple wire routed close the the TDST. It was night time so I was using a bright flashlight to look at this. Low and behold I saw the insulation had been rubbed off the purple wire right at the point where it was routed up against the TDST. I saw a "sliver" of copper strand of the conductor wire, bare and shiney". It was not much, but enough to interact with the TDST which is actually engine/body ground! I though surely this cannot be the cause of my problem, so I tested the situation multiple times in "make the problem come back and then make the problem go away" process methodology. This is unbelievable, but true. I could make the problem come back by firmly pressing against the harness (as is done by the "Vortec" cover) up against the TDST while the engine was idling in PARK. I would then pull the harness away from the TDST shut the engine down and re-start it and the problem would go away. I did this four times shutting the engine off and re-starting it noting the problem coming back (harness pressed firmly against the TDST) and going away (harness pulled slightly away from the TDST). It should be noted that the problem that showed on the dash display WAS: Engine Power Reduced - Stabilitrak error icon light - service traction control message - CEL (Check Engine Light). Every time. With OBDII DTC scanner codes P0220 P2135 P0222. Now that this diagnostic testing has been validated, it is also theorized that high humidity environments also aggravate the situation to cause the issue intermittently, especially during wet conditions. It should be noted also that the TDST showed minor removal of its black epoxy paint covering, but there must have been enough removal to effectuate a ground to the TPS 2 switch B circuit signal output from the TPS so that the ECM/TAC caused these resultant errors and engine de-optimizations through this problem detection. Crazy! Yes! True. Yes! So far now after this fix (harness rerouted and wire wrapped with insulation wrapping) no problem and good idling and driving. I will update later if anything else happens, but I think we nailed this one. I sincerely hope this helps others participating in this forum. (Also thank you KASEKENNY1 for all your encouragement and help.)

KASEKENNY1
Requesting your expert opinion. I too believe that we have nailed the issue. Never-the-less, I did replace the TPS on the throttle valve assembly and also the APP assembly under the dash in the truck. With this, how critical do you think it is that the ECM be reprogrammed after doing this if the truck is running fine now? I ask this because a technical bulletin(s) indicates that this is necessary when the TPS is replaced. I'm referring to GM Service Bulletin 11-06-04-007B and 11-06-04-007C. Do you know, or does someone you know, have first-hand knowledge pertaining to the new software having "real" fundamental, functionality updates relative to the proper operation (enhanced operation) of these assemblies with each other? No hurry on that reply amigo. (If I don't need to take the truck to the dealer for this reprogramming step I prefer not to (if you know what I mean.) Thanks ahead of time.

Thank you KASEKENNY1. I'll be back if the issue resurfaces somehow, but I think we got it this time. As I mentioned before, it is a blessing to know that "we out here" have help from experts like you guys.
Wayne

Just as an update, the truck has been running fine ever since the problem was identified and corrected as communicated in this JUSTPLAINWAYNE / KASEKENNY1 information string. I will try to give at least one more update in a month or so to this site.

First thing that I would do is to read the error code(s) with a OBDII scanner/reader and report the error code(s) on this web site forum. Normally, the error code(s) will help in identifying the source of the problem. The OBDII port is usually at the bottom of the dash. (When your vehicle is safety inspected they connect to it for the emissions test.) Just as an example, I saw an Autel scanner at Walmart for for just $19.99, so they're reasonably priced and they come with instructions on how to use them.

Thank you Ken.

Well, I mentioned that I would "close the loop" on this forum pertaining to the problem and solution that I have reported with my 2010 Chevy Silverado. (Check the JUSTPLAINWAYNE info. String). I'm happy to say all is still fine with my truck and the identified problem was corrected and enough time has now passed to support the fix / solution. No more reports will be provided on this situation, unless, hopefully not, a re-occurrence happens. Thank to to this forum and its participants.