There aren't many things left that can stop it revving under load yet not affect it off load.Partial blockage of the fuel or air supply may still be possibilities.Poor compression often makes starting difficult, but is worth checking.The only electrical thing I can think of and may not have been changed is the TPS, though I don't know if that can fail in such a way as to limit the revs that severely.
I had the same problem once while on a track day. But mine was due to a small era on my part. While on track i got a fault on the rev counter to indicate EXUP problem. So i stripped, cleaned and re fitted, then went back on track. Only to find that it would only rev to about 6k (i think). I returned back to the pits and found that i had put the cables on the wrong way round. ( Schoolboy era.).Have you/anyone done any work recently. Ps. When it was out of gear and on the stand it would rev freely.
many thanks for all the advicewith clutch in in gear bike revs to red lineby not going past 6k I mean you can hear the engine trying to rev past 6 k but needle sticks @ 6 and speed limited to bout 55/60 mph all gearsbike not restricted as been riding it for 3 years and had been riding it long distance & higher speedshave changed fuel stripped fuel filter & pump and air filter
by a process of elimination I figured out that the cable which went from the connector to the side stand switch was faulty and would short out at 8K. Weird but true.So before you start swapping big stuff like crank sensors and stuff, just try linking out all the stuff that could stop the engine at the closest connector to the loom, its worth a try and at least you will be able to discount the simple stuff cheaply and quickly, unlike me.