Throttle Issue on 5.3

I realize this isn't a specific Avalanche question but it has to do with a GM 5.3 engine on my 2006 Envoy Denali with 118,000 miles.  I've had it in the shop (non-dealer) for a week now and they are stumped.  When the tech is driving with the scanner connected he's watching the accelerator and throttle body position.  As the accelerator is pressed, the throttle opens to about 30% then stops even as the accelerator is pressed more so the vehicle stops accelerating.  When the accelerator reaches 90% the throttle opens to 90% and the tires spin!  They tried a replacement throttle position sensor and that didn't help.  This engine does have the Displacement on Demand and I originally took it in for a random missfire issue but the tech says that code hasn't come up again.  Just wondering if anyone else has had similar problems with this on a 5.3.

They are rep[lacing the accelerator pedal with sensor hoping this will solve the problem.  Updates will follow

Replaced accelerator pedal and sensor - no change.  Techs are stumped.

Did they look at what the sweep of the gas pedal is? It should show what position the pedal is throughtout its range.

Need to pull the program from that truck and make sure the tables haven't been corrupted somehow too.

Rodney