This may sound crazy, but the ECU may need to be checked. If you know some one that has HPTuners on a laptop, invite them over and have them plug into your computer. It will show all your lean or rich areas for specific RPM ranges. There are tables set up on the ECU that tell the engine if it needs more fuel or less fuel. You may just need to reload your stock program to get back to normal. HPTuner software will also allow you to make modifications to the tables. This is important especially if you have made changes - CAT back exhaust, Cold Air Intake, etc.