Its an automatic car. My transmission was running fine, I had to replace the rear crank shaft seal. I removed the transmission and replaced the seal. I reinstalled the transmission and topped off the transmission fluid that I bought from the dealership. Everything started fine and there was no oil leak from the seal anymore but as I started driving the car a couple of blocks it no longer shifts. If I turn the car off for a couple of minutes and turn it back on it will shift correctly for the next couple of blocks but then it just repeats the shifting problem again. The car has 160K miles on it.