Problems with my Commanche - HELP ?

Well where do i start. I just bought my 1986 commanche 4x4. It was purchased from WV and i live in PA and well after about the 1 1/2 drive i realized the tranny was slipping horribly and well it started grinding hardcore and then it wouldnt let me go about 6 feet before disengaging the gear and just letting me coast to a stop just to go another 5 feet lol. So i am wondering if i go and get a tranny filter and some fresh tranny oil will it run better ?

Here is some info on it..

Miles - 66,000
Year - 1986
engine - 2.8L Straight 6
Transmission - Automatic

Also the fluid in the truck currently is black as night. And smells quite not so pleasant..

ANY HELP IS APPRECIATED, I am new to jeeps and love the comanche but its looking bleak in less than 24 hrs.

Burnt transmission fluid is very dark and smells, well, burnt. You might benefit from fresh fluid (it's worth a try, and much cheaper) but you may be looking at a rebuild on the tranny. But...since the engine is ok, once you rebuild the trans you won't have to worry about it for a couple hundred thousand miles.