Vexwar

I have an 85 runner, this last weekend I took it camping out here in UT. I took him up parlies canyon which is about a 6% grade. Before I went camping I could be in any gear and the engine would sound fine and no vibrations. When I put it in 3rd, 4th or 5th gear the engine sounds like it is under a heavy load and it vibrates a crap ton. this did not happen till after the parlies run. I am thinking that when I went up it I may have burned my tranny a bit bt I cant figure out what happened. I checked the normal causes for vibrations, i.e. drive line, lose mounts. Any thoughts for trouble shooting would be great.