Your RPM's are way too high for the speed. Even after I installed lighter rollers my DT300 is turning 6000 RPM's at 60 MPH (96 KPH). I'd remove the CVT cover and watch the belt action as someone twists the throttle (on center stand, of course. The variator should move the belt up to the top of the pulley as the engine gains speed. If not, the belt may be the wrong size, which is critical. Compare it to the old one for diameter (length) and width. Tip: You can leave the CVT uncovered while experimenting, just don't ride the scoot on dirty or wet roads until you re-install the cover. You might check to see if your clutch pads are worn out (maybe the clutch is slipping?)