You do not have a vacuum line. This is a 722.6 electronic transmission.
Getting the codes checked is the first step. Also the adaptations. You may have a bad one way roller in the transmission. I also see shifters cause weird problems.
This is one of those things were you need good diagnostics.
Your transmission does not need to be replaced unless there are broken hard parts. Debris in your pan. But it may need to be rebuilt.