Update: I just had that aha moment along with my tps glitch.
simply put... the tac module/app sensor has to match my PCM+operating system. A 2003 pcm/operating system is currently uploaded. The tac module/app sensor is the 2006 oem installed parts.... so I'm going to install 2003 hardware to match my 2003 PCM and kick this P1518 code in the jimmy.
All grounds have been voltage dropped pin to pin. All circuits have been volt dropped from the TAC, APP, and PCM. I voltage dropped every damn ground on the truck and the worst reading I have is 0.02 volts.