Must be either a problem with the bike or rider. Today I had mine up to 167kph / 103mph in 5th gear and it still had more. I was cruising at 85 sometimes at 100 and I averaged 44mpg. It is hard to keep it below 90mph / 145kph when everyone is passing you like you are doing 25mph....

 

I had a bit of an experiment last night on the way to the club meet.Kept the bike in 4th, (5 gears) at about 3500 rpm,70 mph smooth as you like,with more to go,clicked into 5th,keeping the same rpm,bike seems to top out at about 70 - 75.Whack the throttle open,85 -95,is as far as i could safely take it,but at that speed the throttle was only half open so there will be more,no problem.
I also noticed,that because the bike was'nt "vibing" that there was a constant buzzing noise,until i hit a patch of newly surfaced smooth road,then the buzzing dissappeared.So,i would guess that you may be lugging the motor,and the buzzing is tyre noise.
I've had my bike 2 years now,and it's allways been a bit of a love/hate relationship,untill last night.
So i think it is you.

 

Now you've had fun yanking our chains... go ride your "rice rocket" and leave the real motorcyclists alone.

 

Even if it's a Jap Spec Harley with the tiny gears, you'll still be able to plow through 100mph. If you've riden a motorcycle before, then I'm guessing that you'd know that it's not normal to only go 75.

If this is genuine, you're gonna wanna take that pig into get checked ASAP.