Swap 78 nova has been running over a year , everything from 09 Silverado 5.3 with 6l80. Took car out yesterday Memorial Day running fine get on freeway , then I noticed car wouldn't shift out of 4th gear at this time I have throttle so head home, 5 blocks from home and no throttle but engine still running. Finally make it home, disconnect battery for 10 minutes reattach, throttle responds so I drive around the block goes through all six gears , then no throttle response again so I repeat process with battery but same results after a short drive no throttle.

 

I think I would have converted to drive-by-cable already.

When the throttle stops working, check for codes. You might be losing TAC signal or ground (it was ground in my case).

 

I pull code po641 open circuit. So am checking the harness and grounds.

 

http://www.camaro5.com/forums/showthread.php?t=360258
couple threads out there about back feeding sensor voltage.