1996 Dodge Caravan Transmission slipping

I have a 96 Grand Caravan with approx 150k miles. Today I was driving in the neighborhood and the transmission felt like it slipped out of gear. I think it was right after I went over one of the speed bumbs in the road, but I may be mistaken. When I got back into the van to drive, everything seemed fine. The transmission shifted through third fine and then slipped sirectly to nuetral. It jumped back down to thrid and back to nuetral again. I slowed down and it felt like it shifted down to second. The RPM's were about 3k for 35mph. I drove slowly to a gas station and cehcked all the fluid levels. I did notice that when I moved the gear shift to park that the lights appeared to move with a delay, but it may have been normal and I never noticed it.

When I got back onto the road the transmission again seemed to shift fine until it got to third. Then when I tried to slip into 4th, it slipped in to nuetral again. When I slowed down again, it had a little shake when downshifting from nuetral to what felt like second. Each time after the slipping incedent, the gear stay in second and will not go back down again until I turn the vehicle off.

The transmission was completley rebuilt about 50,000 miles ago and I instantly thought it was going out again. They only reason that I think there might be something else going on is that it start to shift fine each time I turn the vehicle off and back on again. Any suggestions?