Yah! These are high rev'ing bikes! As stated you should have no problem hitting 90 in 3rd. They should top out at 120 - 130 in 5th which is and OD gear. I've had mine up to 115 with more still there but I chickened out. Also as mentioned they have a rev limiter so you can not over rev these engines.
To tell if the differential was swapped out to a VMax, try shifting into 5th at about 45 - 50 mph and try accelerating rapidly from there. If it hesitates, bogs down, etc you have a stock differential. If it's a Vmax it will respond normal.
To discover what the rev limiter sounds and feels like pick a gear like 2nd and twist the throttle wide open and hold. You will know when it hits the limit, it will act like you broke the engine, but you didn't.
Maybe you aren't running on all 4! With the engine cold, start it up and immediately feel all 4 pipes. All 4 should feel warm after a minute of less. If one or more stay cold you have a problem!!