Help wanted dt125r power problems

[CraigDt125r1999]

Hi all my name is Craig, I am new to this (newbie I know :L) anyway I recently bought a 1999 dt125r which runs great until 5th gear which it will stick at 9000 revs(makes 6th useless) at 60mph I've de restricted the airbox which helped acceleration and I've pulled out Reed switch ( not cut just tucked away)which did absolutely nothing I thought that would fix it, I know my powervalve is restricted as the holes don't line up which I will sort, it has the standard expansion chamber which is de restricted and a dep silencer but 60mph seems abit slow as I know these bikes have a lot more to give, any help would be much appreciated thank you