Codes PO2004 and PO174 after replacing the engine?

Hi, I had a used engine put in my truck listed above back in April. Right afterwards the check engine light came on, po2004 code. This truck has 2020 tags and I need it to pass smog so it can be tagged with current registration. I bought it for $7,000 in December and spent about $5,500 for the used engine along with insurance and timing guide and tensioner replacement. A different mechanic shop, a specialty transmission shop, has been trying to fix the check engine light for 2 weeks now. I replaced and flashed the computer, new imrc valve actuator, and the wiring was checked for continuity. I took the truck home last night and the Check Engine Light came on again, just not the additional po174 which was caused by the initial po2004 code when I first brought it in, so only 1 code instead of 2 if that helps. Please, please give me a list of possibilities that this could be so I can run it by them and hopefully be of assistance in troubleshooting this very tedious Check Engine Light code. Linkages, new harness, bushings, new intake, solenoid, lever arms, etc. Please list what should be replaced in order of importance and what is most likely wrong as it seems like this is going to be part swapping at this point, but I don't care, I desperately need it to pass smog. They fixed the Schraeder valves and refilled the Freon, so it blows cold AC and replaced the shifter cable so I'm sure they are a reputable shop, but this Check Engine Light isn't fun for either of us. Please, please help!