First of all, just wanted to say hello and thanks for the join.
Just bought a 2010 Lucerne with the 3900 engine in it and it has a little issue that I can seem to figure out. I’ve replaced the throttle body and the mas, map sensors and gas pedal with no change. Under very light throttle less then 1/4 car operates fine. Anything over 1/2 throttle car is fine, even to the floor is fine. But if you go 1/4-1/2 throttle, the car acts like you’re fully releasing the throttle and putting it back on but your foot never moves. It’s really weird. Never had a vehicle do this. Nothing has help or changed it. Car runs great as long as you stay out of that throttle area. Scanner says everything is good. TPS % doesn’t change. No codes at all which it throwing me. Please help.
Thanks in advance!

 

A calibration on the pedal and TB may be something to consider. Cleaning the MAF, air filter and checking that the intake hose, clamps are secured. A professional scan might be inorder vs parts cannon approach as most consumer OBD2 scanners have limited functions.