loose t-case linkage, loose motor mount,or other?

Alright here's my problem so i'm wheelin' about 3-4 months after I've had my xj down at our 7 acres takin it easy in 4 high rip pretty hard here and there pull out on to the street put it back in 2 high tryin to clean a little mud off the tires (mind that i stop every time i change from 2-4) i stop put it back in 4 high and start to take off and it starts to make kind of a grinding noise and it sounds like the rpms are getting higher so i slam it back in 2 high it didn't stop but started to die down so shut it off started it back up tried 4 low and it seemed fine i got on it pretty good (pretty good being half throttle in both cases) nothing strange or out of the norm, I tried 4 high a little later and it seemed ok then but i wasn't really trying to terribly hard. So a few months later then we get a couple inches of snow and want to test it out it took off in 4 high fine and i started down a hill in 1-2 of the automatic and it does it again so i shut it off start it back up and put it into 2 high and headed back home. My friends dad (keep in mind he's not just some guy maintains cars here and there he's worked on them all his life and as a side job if you think it could be something other than) said it could be the linkage needing adjustment or maybe a bad motor mount.
So if anyone out there could help me it would be greatly appreciated considering that I love to go wheelin.

Also my xj has a 3" rough country lift and stock drivetrain if that maight help.

have someone inspect your transfer case chain for streching NOW!!!
I had the same kind of situation and id not take care of it. the grinding sound was the chain jumping off the sprocket and sending tiny bits of shrapnel around until it eventually destroyed my transfer case to the tune of 1100 in damage. unfortunately I now know that a new chain wouyld have only been 150

Well, inspect your linkage: see if it's missaligned or loose. Also inspect teh motor and engine mounts cause he's right: if they're worn they will make the linkage misbehave big time, especially when you get some flex on the rod that goes between the body and tcase mount.