For whatever reason my motorcycle doesn't want to go past 93 mph and it's acceleration is weak compared to when I first bought it used (I accelerate at about the rate of a standard 4 door car). I have full access to my rev range in neutral, with the clutch in, and in lower gears but it falls off as I approach higher speeds. For example, I can take 1st gear up until around 60 mph, very close to the red line no issues at all. But say if I'm in 4th gear, I can ride up to 93 mph and I can't get past that no matter how much throttle I give. The RPM will be stuck around 8k (unless I pull in the clutch) and if I shit up to 5th gear, the revs will drop but maintain a maximum speed of 93 mph, same story with shifting up to 6th gear, further RPM drop and I can't get past 93 mph. What are some of the things that could cause this issue?