1986 420 SEL shifting roughly

My wife took the car to Missouri from Indiana. When she came back I could feel that something has gone wrong. She said that she felt that while driving in the mountains, she felt all of sudden it started shifting roughly.

Now I am concerned if this is a major expense or not. As I am slowly accelerating, I could feel a noticable jerk everytime it shifts from 2nd to 3rd and then from 3rd to 4th. When I slow down at the light, the down shift to 1st is also very noticable. Any help would be very apperciated.