Shifting problem

In the last month or so I have had to let off the gas to get it to shift to 3rd, my son drove it and now it want shift into 3rd, the fluid was low but that hasn't helped do I need to relearn the trany or what else is needed

 

Good morning and welcome. First, we need more info on your truck. Engine size, miles, assuming Auto trans but need verification.

Also, have you searched the threads yet? There are quite a few on here

 

I’ve run into a similar situation in the past with hard shifts and switched to all synthetic. Helped take the edge of the hard shift. So, verify you have the fluid at the right level if you haven’t yet. The solenoids tend to not shift smoothly with too low fluid.