Feels like clutch slips in high gearwhen trying to acc.

make sure there is 3mm play on the clutch lever , select 5th gear while engine is running and press the rear brake to stop you moving away ! with a little revs try and set off , if clutch is worn it will slip and not stall the engine ! if this happens then replace the clutch plates !

The slip is likely always there you just feel it the most in top gear because that is when the most stress is on the clutch pack inside the transmission. You will need to have the transmission overhauled in most cases to correct this.

If it feels like the clutch is slipping, chances are it is. If there was a problem in any component that has internal gears, you would have grinding noises. Gears cannot slip. As the clutch wears more you may hear grinding when you try to change gears but that is because the clutch won't fully disengage so the gears are spinning too fast to shift properly. Before that happens, have the clutch replaced.

Sounds like the clutch is slipping. If the clutch is bad, it will slip in high gears (4th & 5th) but seem to work fine in lower gears. Clutch probably needs replaced but have a mechanic check it out first because it's a fairly expensive job. If your clutch is actuated via a cable (not hydraulic), it may just need adjusting.

TEst for slipping clutch is travel about 30 mph. press clutch, shift to 3rd, rev engine pretty high and release clutch, at the time of clutch release, floor throttle. If the engine continues to race, clutch not grabbing porperly, if the clutch works properly, the engine will be slowed and engauged.
You can always get a 2nd opinon from another shop.

the 85,000 mile coutch worn out issue dependes entirely on driving habits of the operators.

Well i would say the clutches have sat dry to long. You may change the oil and it solve the problem but more than likely new clutch discs.

The clutch plates are grinding

From the sounds of your riding style (wheelies, etc.) you have burnt out the clutch.
No matter how much fun you think it is, Yamaha never designed them to be a toy to do wheelies. It is a sportsbike designed to go round corners fast.
The only silver lining is, hopefully the cost of replacing the clutch will stop you riding like a fool in future.

ya used the wrong oil in the gear box, the clutch is slipping, to fix thhis it could be as easy as proper oil replacement in the gearbox or as bad as new clutches, the oil you use in a bike is VERY important as some cause clutches to slip and others to grab depending on the weight.

yes because there is no pressure for the clutch so thats ur slipping feeling try looking at the seal.