Transmission slipping

Transmission started slipping all of a sudden. What would have taken me twenty minutes to get home ended up taking me two hours to get it home. I had no problems what so ever and then the transmission just started slipping. When I first crank it up, it will take gear, but won't go to fast or to far and it starts slipping again. When it runs for a few minutes it won't take gear at all. I really don't think I need to change the whole transmission, but I may have to. From everything that I have looked up and found on it, it's in limp mode.