Check Engine Light

[96GTPRT]

Ok I had a Flowmaster American Thunder cat-back installed on my 96 GT a year ago next tuesday. ( i know its creepy that i remember but theres a reason.) Anyway, ever since, my car has had the check engine go off and on every so often. I took it to school and used the OBD II and it gave a code for Rev limiter and high speeds reached. (opps!) I cleared the code but the light continues to go on and off. When it went to the dealer, they found nothing and the light wasnt on at the time. I recently passed Illinois emmisions testing and the car runs fine, no problems at all. Does anyone know why my light is going on. I only have bolt on mods, most of which were added after the cat-back. Is there a sensor that is really picky or something that is setting the light off because of the cat-back? I think that may be it cuse my friends Honda has the same light on because he had a cat-back put on but the dealer said it was just because the Honda sensors are really sensative. Any help would be great. Othewise, when i get my X-pipe with cats im just gone get MIL's to cuse the light is starting to bother me. Please help!