I don’t know what “alternate gear across from ‘3’” means. The car hasn’t had a transmission fluid exchange - usually owners who keep current about maintenance do it at around 30k, so you bought it with too few miles on it for the previous owners to have done it, and since you say you don’t know the transmission service history, I take it that means you haven’t done it either. Driving a car with 70,000 mile old transmission fluid is a good way to make the transmission misbehave. Get the fluid exchanged (not flushed - exchanged. There is an important difference) and see if that makes it better.
Also, you haven’t ever told us what exactly it is doing that has it in the shop for the transmission in the first place. . .