Not in the US, im in Scotland. Im 170lb's myself. My scooter has the 50cc gy6 139qmb 4 stroke engine dont know if your scooter is exactly the same engine. I get 45mph easy, even in the wind, normally 45-48mph on flats, occassional 50+ on a good day.
Currently im still on my stock air box, stock exhaust and an #82 main jet too, so I could still gain a few mph if I fit a k&n type filter im sure. Fully derestricted it, fitted race variator, 5.5g rollers and a 1000rpm torque spring in the rear. Pulls smooth and pretty strong now to 45mph easy, normally sit at 45-48mph all the way to work.
You must have something holding yours back still, jst dont know what if its not your belt tho. Hopefully someonewho owns the same scooter can give us their opinion and tell us how fast their scooter goes, sure they must go faster than what your getting.