Trouble uploading new bin LT1

I have a 94 LT1 that has been transplanted into a 95 K2500. Was originally trying to run the engine off the LT1 pcm and the trans off the truck pcm. Ran into some issues.
I've since rewired the transmission to the LT1 ECM, added a signal wire for the torque converter PWM signal and trying to upload a 95 Bin file.
I'm using eehack. I get a good connection, the pre-upload tests are good. When I hit upload, I get an error ERROR TRYING TO APPLY VPP VOLTAGE.
Any help is much appreciated.

probably need a bit more battery voltage at the ecm. it's picky for a reason. make sure all accessories are turned off and voltage is dead stable and at least 12v at the ecm

Thanks Steveo. You're the man.