Buick Regal Has No Power

2002 Buick regal 3.8L.

Question:
engine won't run over 4000 rpm with out missing. Runs good on flats and hills as long as you keep the rpms down. Starts good.

ANSWER:

There are several things that can cause this.
1. Low fuel pressure
2. Faulty ignition components such as coils, wires, plugs.
3. Faulty MAF sensor. Usually will have a check engine light and codes though.
4. Plugged catalytic converter.
If the above things have been checked, then what you describe sounds like a plugged catalytic converter. If that is the case, GM has a special policy that may apply to your car that will replace the converter at no cost to you. This depends on the VIN # of your car. You are within the mileage range for this special policy, if your car is within the correct VIN # range.