1999 Buick Lesabre Rough Shifting

I have been experiencing rough shifting in all gears on an otherwise great car. It has had a very easy life but this is worrying me. It jerks from park to drive and as it shifts through the other gears. This may sound crazy, but it seemed to start giving problems after I pulled up to far against a curb and concrete curb(tire stop) scraped or hit under the car. It's been like this now for close to a year, I tried some Seafoam transmission stuff in it, but no luck. Can you help me out?