91 explorer tranny slip

Just got 91 exlporer 4.0L 4x4 a few days ago knowing that it has transmission problems, it slips so much that it won't go more than 100 feet or so. Last owner did a tranny oil change but it didn't help much. I was wondering if maybe it might be something simple like a filter or an adjustment I can do.Also I have a 78 ford f100 (4.9L -straight 6) with a good transmission ,will it bolt onto the 4.0L explorer engine? Just seeing what options I might have to get this explorer going again. Any help would be great! thanks. Ray

I don't know if you posted this in the the Explorer forum BUT, if it's slipping that bad, it's time for a rebuild. and the transmission from a F-150 won't bolt up. Your best bet, find another Explorer that's wrecked or one out of a Ford Ranger anything prior to 1995.