As for the RPM issue: I installed a 1015 spring, 14g weights and clocked to C2. That gives me a low gear shiftout of 6800 RPM, a high gear shiftout of 6200 RPM and a 30MPH cruise of 5200 RPM. It pulls just as hard in high gear now as it did in low before. High as it seems to rev, it gets very good fuel mileage for an ATV, about 30 MPG on relatively flat ground.
My fuel gauge, however, not so accurate: when it reads empty, I actually have about 2 gallons left in the tank, maybe 2.2 gallons. I have gone 130 miles without refueling or running out of gas, but it took every bit of 4 gallons to fill it back up!
It sounds like it's over-revving, but the motor is operating in its happy range!