95 trans problems

i have a 95 suburban 5.7tbi 4x4. I cranked it this afternoon and put it in reverse and it felt and sounded like i backed into another car. I now don't have reverse but it will go in drive. It acts like it's in neutral when it's in reverse and whines a little. The same whine is there when i put it in drive but it works. I've only moved it about 20 feet so I don't know if any other gears work and haven't tried to put it in 4wd. I drove it home from work just a couple of hours before, it's never had any transmission problems before. I am somewhat literate on 2wd trannys but not 4wd. I do have a lift, trans jack and whatever tools i need, I just don't know where to start. There is fluid around the linkage where it goes in trans, but not enough to leak down around pan bolts. Also looks like the rear seal is leaking and slinging fluid just before u joint but fluid isn't low. Anyone have any suggestions

How many miles on her? You said the fluid was the correct level, but what color and how does it smell? Burnt? You could drop the pan and check for metal shavings in the fluid/magnet, which is usually a bad thing. Just my thoughts.