Full throttle in top gear going up hill, if your revs rise but you start rolling backwards then your clutch is slipping :biggrin
Seriously, if your giving it the beans and there is no extra drive with the revs increase than thats a sure sign of clutch slip, it should feel fairly obvious if thats whats happening.
It's fairly easy to tell if the clutch slips under load.
You'll actually sense it too but if your not technical then you'll most likely disregard the sensation. (No offence meant Tim) LOL
Find any stretch of quiet road and get up to about 20 - 30 mph, knock it up a gear so that the engine RPM drops to around 1500 - 2000 RPM, finally knock it up another gear so the engine labours quite a bit and slowly wind on the throttle.
This will tell you if your clutch is slipping or not.
Slipping is defined as when the engine RPM gain is not relative to the road speed increase. Can be experienced when your engine gets hot during a trip round a busy town etc....
If during the above you notice that the engine races e.g. Revs increase rapidly but road speed does not.
Then it's time for a Barnett clutch :doug
(I'll pop over and fit it for you mate, just feed and water me and give me a place to lay my head and we are sorted) LOL
I always found my clutches started to slip more in higher gears.
My old kwak started to go but it was find for normalt riding but as soon as I gave it some in 4th and up and past 8grand the rev needle just shot up lol.