Transmission is experiencing rough shifting?

A few months back my car threw a code that said, shift solenoid from 5 to 4 was malfunctioning. I stopped the car, turned it back on, and the code went away. I didn’t think too much of it, because the code never came back, and I didn’t hear, see, feel, or smell anything. However, yesterday I took the car over a mountain pass, and my car started to shift rough. The code also popped up again. We assumed that my transmission was low on fluid, so it overheated when I was taking it up the mountain. The car runs beautifully if I drive faster, but if I am just driving in town, it shifts a bit rough now.