LT4 8L90 issue

[vet57air]

My friend Kelly and I both have LT4 8l90 crate packages. His is in a 72 Blazer, my in a 66 C10. Every since he started his he has had a check engine light. Codes are to do with the transmission solenoids. 7 codes in total. The Blazer runs and drives without any issues. He has had techs look at it and delete the codes but they always return. I bought HPtuners for my setup to change the trans shift points. Worked very well. He has talked to GM phone tech and they think it is software.
Kelly called me and I looked at the diagnostics and tried to clear with no success. I downloaded his tune and saved then uploaded my original TCU program to his. No change. He drove for a couple days as these codes are permanent and take a few cycles to clear. I just uploaded my ecu and tcu program to his successfully then immediately checked the diagnostics. The codes remain. Our next plan will to be replace his TCU, but if anyone has any ideas let me know.