DJ5 Postal Jeep

Hello. My question is for 1977 DJ5 postal Jeep. This morning it fired right up but I noticed it seemed to struggle changing gears. It is an automatic. I came to a stop light and the Drive shift wouldn't work when I pressed the gas. The engine sounded fine. The reverse wouldn't work either. Someone pushed me off the road to get out of the way and eventually it worked again. I drove it home and heard sounds like it was struggling to switch gears or something. Sorry for my lack of terminology... I am just wondering what the basic problem could be before I take it into a shop. Thanks