1996 Oldsmobile Ciera acceleration

My car has problems accelerating. When in park/neutral it will rev about 50% of the time with no problems. The other 50% of the time, it sputters and backfires and eventually starts to rev without problems.
When in gear, however, I have to lightly feather the gas pedal to get the vehicle to move. (If I floor the pedal, there is no response at all.) Even when lightly feathering the gas pedal, the car will still buck, sputter and backfire sometimes. Going up hills it takes the car a while to shift to third gear unless I let off the gas pedal, but then I lose my momentum and have to wait for the rpm's to build before the car will accelerate.