is it just 3rd gear? i've read about some kind of "third gear lockout"...i.e. under full throttle, there's some sort of electronic controller maybe that curtails the shifter movement...i don't know the validity of this idea, but i do know that when i first got my truck, and was "learning" how it fealt (cuz we all know it's not quite the same as your bracket racer), and after dynoing the truck i noticed that i was shifting late based on the hp and tq numbers...needless to say, i shift around 48-5000 rpms, and i've never missed a gear since (had it 18 months...long enough to know)....again, i don't know the validity of the "lockout", but hennessey (of course) sells some kind of something to "prevent" that...don't know if that helps...or could just be some brass in the trans