2000 Ford Contour transmission slipping?

My husband just purchased this car from private owner and had only driven it around the block as there was no insurance on it. On the way home after about 5 miles, he said the car acted like the transmission wasn't working properly. It would cut out and then catch back up. We knew there was a radiator leak due to a minor front end hit but he doesn't think that's associated with this problem. Are we up the creek on this one? This problem only appeared after the car was warmed by driving about 5 miles. Thanks so much.