1999 Dodge Grand Caravan transmission issues

I have a 1999 Dodge Grand Caravan with approx. 94,000 miles on it. Here's my problem:
I was driving down a highway with the cruise control on at about 70mph when all of a sudden there seemed to be no more gears.( Meaning I stepped on the gas and the van refused to go any faster). I pulled over to the side of the road and tried to go forward, it did but then the engine reved but the van did not move any further. I did the same thing in reverse and it did the same thing. I shut the vehicle off and did the same thing, which the van responded with the same thing by only going a few feet before not wanting to move. I checked my transmission fluid and it was full and it had no leaks to be seen. While the van still running, I tried to put it in drive again this time the engine reved up and then you heard the van finally shift into gear but would not go into the next gear. Need less to say I had the thing towed home. But before I make any rash decisions by changing or rebuilding the whole transmission, could there be a simpler, cheaper problem at hand? I mean this came without warning, and this van had no prior issues up to this point. Please help me with any suggestions that you might have for me. Thank you for your time.