I have a 1990 K5 Blazer and as I was driving down the road and hit a small road bump on the highway my tranny (700R4) slip out of overdrive. I had to let off the gas and slowly throttle it and it was hookup again, but each time I hit a small bump it was do the same thing. I finally down shifted to drive and it drove fine. Any clues, ideas or thought on this.

Respectfully Steven