Honestly put tractor in mid range gear idle to low medium rpm. Lock the both brake pedals. Hold your foot on the brakes tight. Let foot off clutch. If the clutch is slipping the motor will not die but will draw down rpm. If the clutch is good the motor will die immediately. We did this trick on every tractor we bought to determine clutch life. Just don’t do this all the time it’s spot check activity at best. Make darn sure nobody is around tractor when doing this is activity it’s just plain dangerous if your not experienced on this activity. If the clutch is slipping push it in and shift tractor to neutral. Shut down tractor and inspect free play on clutch per manual requirement. No free play in clutch you will experience slippage. If free play is ok pull off access plate inspect clutch make sure it’s dry if oil soaked this will cause slippage. If not wet then verify lining it may be worn out , typically 700-1500 hours if using tractor hard. Wear is different on all tractors some can go 3000 hours never have an issue. Clutch life is user dependent especially if doing front end loader work. The more use equals wear if clutching a lot changing directions.Whether this is correct I do not know but an old tractor mechanic said if you put the tractor in the highest gears and then push against a strong tree if the tractor stalls the clutch is not slipping, if it just motors on then there is slippage. Only saying what I heard.