Hope someone can help

Hope someone can help.
I will gladly donate a few bucks if someone out there is knowledgable and has access to a FACTORY KIA SERVICE MANUAL and is willing to email me what I need to fix the vehicle I have listed below!

I have a 2004 Kia Rio 4cyl, Manual Transmission.
No Power Steering and No A/C with 89,000 miles.
This is a bare bones KIA RIO no power options at all!

PROBLEM:
It stumbles ONLY when it reaches operating tempature.
Runs normal as long as the temp gauge needle is sitting on or close to the C. As soon as it warms up, the engine stumbles,
NO Power and very difficult to get moving even in 1st gear.
I've been able to check for codes with a limited use scanner.
Code P0068 was present and the check engine light was on.
I checked the Throttle Position Sensor and found no problems with it Hot or Cold. Also removed the Mass Air Flow Sensor.
Cleaned it and tested for open circuits, but found nothing wrong.
Checked and cleaned the PCV valve and replaced the Spark Plugs as they where the originals. Also checked the fuel filter and replace it too as it was also original.
After clearing the codes I drove it again.
As soon as it warmed up it had NO POWER.
And the P0068 set again after lopping it back home.
Am I missing something?
Is there a Trouble Tree for this code that would help me
figure out the cause of this condition?
Any ideas would be most helpful.

I have worked on many makes and models over the years.
Most familiar with GM cars and Saturn S cars. (Worked for a Saturn Dealer for over 10yrs)
I am retired from wrenching full time since my back gave out.
I was hopping to get a little professional courtsey with this problem if possible.
In the Saturn factory service manuals, they had trouble trees to help with the diagnostics. Haven't seen anything like that for KIA.
Do they exist? If YES, could someone send me the trouble tree for P0068?

Thanks for any and all help.