1997 blazer tranny issue p0758

I have a 1997 blazer with the 4l60e and it's throwing the p0758 cel code. i have researched all the common problem's yet i have not found my problem. i have replaced both the 1-2 shift solenoid & the 2-3 shift solenoid, i have replaced the internal wiring harness inside the pan, i have replaced the ignition switch, i spliced the old 20 pin harness connector off the engine side of the harness and replaced it with a new 20 pin connector. If i take off and have my cel cleared it take's off in 1st gear and shift into 2nd gear perfect but will not shift into 3rd gear until the cel light comes back on.... then it will not shift into overdrive until i have once again cleared the cel while drivng.... so pretty much cel on means it will take off in 2nd and shift to 3rd and that's it from what i understand this is called fail safe mode. im at a loss of what else could be the problem somene please help before i take it to the auction and loose a bunch of money.

the ecm may be bad, or there is a problem with the wiring somewhere....

it is not receiving the correct signal for the solenoid, after the vehicle has warmed up, which sets tht DTC and failsafe mode