mine wouldn't rev past 6000 rpm when i got it but that was because it had lost power from the battery at some point and reset to original factory values, rev limiter at 6000 rpm and speed in kmh not mph. Are you getting a red flashing light on your dash when you hit 6000 rpm? Or does the needle only go round to 6000rpm when you switch on, this, from what i have read, is what the rev limiter is set to.
Just need to reset the rev limiter if that's the case.
bought my 04 with apparently 18567 miles on the clock, which is shown on the MOT certificate. Unfortunately for the form but fortunately for me, that was actually in kilometres not miles so now i have an 11000ish 04 Tuono.:thumbup