Clutch slipping?

[sleam]

Help! A mechanical issue I need your ideas - please...When driving the 72 in the mountains of Colorado the other day, a couple of intense hours in 80 degree weather, 9000 ft altitude, the engine suddenly acted as if I'd put it into neutral when in fourth, revs up no power then back to driving. Did it a few times in fourth so I turned back before the pass. Yesterday, drove 200 miles or so, hot day, 7000 ft altitude, fine for the first 180 miles then the last stretch home it would do the same in 4th gear on hills, then any thing other than downhill, and then in 3rd gear, unable to drive. It's now parked at a mechanics but he's not a Landy man, so I wanted to ask your advice too.
- Clutch feels the same, strong, perhaps not enough play before engaging.
- Did it overheat and so stop working? That was the tow truck guys suggestion.
- there is a bad leak at the prop shaft, would that make the difference?
- and what do I do now???
Thanks

[NC_Mule]

Random thought. Is your bell housing drain plug in? Does it feel normal when you take off in first gear. What if you drive down the road foot on the gas and then apply pressure to the brake. Does it slip then?

[I Leak Oil]

Find a good hill, start in 1st, get a good head of steam going, shift to 4th and give it hell! Does it rev or die out....?

[sleam]

- It feels normal driving until I'd been on the road for a couple of hours in heat and then revs and no driving power.
- It revs...
what about the push rod adjustment? Someone suggested that might be it, before taking out the clutch.