This happened first time a week ago was just driving up a hill truck had shifted fine from 1st to 2nd to 3rd and it was revving its self up and not wanting to shift into 4th gear then finally it just gave up trying to shift and it started revving the engine like it wasn't in gear. I put it in neutral put it back in drive didn't work so down shifted to 3rd gear back to drive finally got it to work...didn't happen again until today was again coming up a slight hill and got almost to 4th gear and started revving up the rpm's and wouldn't shift so same thing as I did before and got it back in gear. I slowed down to turn and it shifted just fine back to 1st gear and then worked fine all the way home...I had the transmission rebuilt in February of 2010 so I don't think its that but its worrying me to death as to what it is. So tired of throwing money away in this thing. Just replaced my spark plug wires today still gotta fix my seat...so time for a new vehicle!