could be a variety of things, what ets are your running?
you could be launching harder then the others,
too small of a carb,
too small exhaust,
ignition isnt timed all the way, keep running passes slowly bumping the timing up until you hit your fastest mph then you have the perfect timing for your combination.
you could have a torquier cam, a lower rpm powerband when others in your class have higher.
to much spoiler if you have one
to much gear like Tod said
etc....