Scotty, 

I own a 2011 Silverado 5.3L 1500 with 135K miles and trouble code  P2122 Throttle /pedal position sensor/switch D - circuit low. It has an automatic 6 speed transmission. So far, I've replaced the foot pedal assembly with sensor, replaced the electronic throttle position sensor unit on the throttle assembly, cleaned the throttle assembly, applied diaelectric grease on TPS contacts and it ran fine for a year. Today, this same code came back on and of course everything else that happens when the vehicle goes into safe mode associated with this code such as reduced power, stabilitrak goes off-line, and the vehicle basically goes into limp mode.

One thing that I've learned is that this condition happens when the humidity is high in the summer, early morning cold engine start. I usually disconnect the TPS harness connector on the engine, make sure it has dielectric grease, reconnect and the vehicle drives fine but with the check engine light code still illuminated on the dash until I clear the code or clears itself. The only thing I can think of causing this issue is a frayed wire, or loose ground somewhere?? 

Any input is much appreciated. 

Thank you, 

Norman from SC