1994 Dodge Dakota Transmission problem

I was traveling down the road in my 1994 Dodge Dakota approximately 45mph when the transmission stopped pulling. I pulled over the the side of the road, raced the engine, but truck wouldn't move. I switched the truck off, restarted it, put it in drive and it moved forward but when it shifted from 1st gear, it stopped pulling again. I had the truck towed to my house, cranked it up and put it into drive. The transmission seemed to function normally for about a mile, then stopped pulling again. Any ideas as to what could cause this problem? Appreciate any help.