I have a 2002 Monte Carlo LS with a 3.4 and yesterday I started to notice a problem in acceleration. I start pushing the pedal down and it will hardly respond only going up to about 2000 rpm and getting upto only 30 mph after pushing the pedal all the way down it jerks and accelerates but will start revving at 4000 rpm and get up to 40 and won't change gears. I'll let off the pedal and it'll change gears but then it'll barely accelerate after that losing rpms.

 

Have the catalytic converter checked. Blockage in it will cause your symptoms.