Hi, I have a 1992 Pontiac Sunbird SE, 3.1L Multiport V6, 211,000km. The car runs and drives great but the engine seems to misfire when floored. It sounds almost as if it is hitting a rev limiter or something. If you ease into the pedal it gains rpms fine but if you floor the pedal it sounds like it's hitting a rev limiter. It also does this under heavy acceleration, The car also doesn't want to go above 3000rpms. My friend has the exact same car and her's doesn't top out until 6500rpms. It never did this before the engine was rebuilt, and it only has 20,000km on the new engine. We tried changing the plugs (what a NIGHTMARE), plug wires and air filter but it made no difference. Any help would be greatly appriciated.