new problem developed recently...car is an allmotor h2b

at the track reving the car up with no load to do a burn out or launch the rpms will not go higher then 7500ish...the redline of the car is 8800. the other thing i noticed is from 5500 to the 7500 the engine's tone changes and the revs rise more slowly. after the launch down the track the car has no problem redlining while shifting....its on an s300...stock ignition...theres no two step set...just been holding the revs at 8k and launching....any ideas...theres no codes or cels and im stumped