Hi everyone

I have bought a used xt660x 2006 model about 30000 km and i am the 3rd owner now...
The problem i have is when i want to make a fast acceleration 0-100 i start at high rpm with fist gear and then i try to shift at second gear but some times its hard to shift at high rpms and i can hear the gears from 2nd to scratch.And some times again with high rpm trying to shift from first to second gear,i can shift second and then it downshift its own to first gear and bike goes to revlimit...at normal ride i have no problem with shift....Anyone have the same problem? Please help