Ranger throttle limiter?

I have a 2003 RaNGER 2.w.d. AND IT SEEMS LIKE WHEN IM IN 5th GEAR, the throttle wont allow the motor to fully wind out to get all 5th gear has to offer on its top end. I can push the throttle all the way forward but it seems it doesnt effect the motor any more....almost as if theres a built in safety device that wont allow 5th gear to reach its full potential or allow the motor to get enough rpms to make 5th gear top out...

is there a way to fix this ? I feel as though im missing out on about another 5+ mph on top end once im in 5th gear because I cant get the motor to rev up past a ceratin point reagrdless of how far forward I push the thumb throttle