Check tps voltage with a multi meter. If it goes above a certain value it will drop out of pe. Throttle position in the scanner will still show 100%. I think it was 4.5 v but can't remember as it was a while ago I dealt with same issue.
That should be check tps voltage at wot.
Just experienced this today on the dyno. Anything over 4.75 tps volts at wot will cause it to go stoich at 4200 rpm. It needs to be over 4.3 but under 4.7 at wot.
apparently another way to cheat it rather than adjust the throttle sensor is to increase the max tps voltage ( TPS high Fail) in engine diagnostics section