shoulda gotta stick instead of auto, obviously if your Nitro is revving up hard, but not picking up speed, the engine is producing power, its just not getting trasferred to the wheels, which means your getting a tonne of slippage. My 6spd picks up speed pretty decently for a 3.7l V6, and I don't get any hard revving unless I'm stepping on the gas in neutral. Have your tranny looked at.