99 monte no power acts like its missing

I have a 99 monte carlo with 125k and the 3.1l. While accelerating it seems to have no power, also when you get up to speed in bucks and jerks going down the highway. My cheap scanner does bring up any codes but my father in laws scanner brought up a code that said the PRND12 range sensor was bad, and it said that at the moment it was in 3rd gear (even though the car was in park in the driveway). I replaced the range sensor and it changed nothing also he lives 90 miles away so i have not had the chance to put it on the scanner again. It has new plugs and wires and neither scanner said anything about a miss, even though thats what it feels like. Any help would be greatly appreciated