I agree with the TPS
Get a voltmeter and check to see that the volts go up smoothly when you open the throttle.
My daily driver olds is the same way, if you floor it the service engine soon light comes on and it doesn't want to go... 80% throttle acts like it's floored. When I hooked up the voltmeter the volts jumped all over the place. actually reads 0 volts at WOT. I haven't been able to change it, since the geniuses at GM put a weird bolt on the throttle body and I have to take it off to get to the TPS!
