My 1994 Isuzu Bighorn V6 SE Wont drive?

With my 94 isuzu bighorn when you put it into any gear the engine sound will change like it usually dose but the car wont move. Somtimes it will move a few meters but if you rev it will stop. This problem has slowly started like when you first turn the car on it didnt used to change gear properly then it turn to when the engine got hot the car would stop moving and you would have to wait for the engine to cool down and then it moved on to whenever you let go of the revs it would stop and now its at this. Could it be a belt or somthing, Ive checked the shaft and transmission fluid and the gearbox seems alright from my point of view although i dont know much, Can anyone help?

Harley
January 2010