Locate vacuum line from transmission

That hose is a vent hose only. Generally it is a short piece of hose about 6” long, attached to the vent tube and some of them go all the way to the back of the transmission and end. The shifting problems have nothing to do with that hose. The shifting problems will require a scanner and possibly a pressure gauge to diagnose. Could be as simple as a bad solenoid, but you have to read the codes in the diagnostic memory and start working from that information. Pull the dip stick and see if the fluid is dark brownish colored and smells burned. Honestly, if the fluid smells burned or brownish in color there is a good chance the transmission will require a rebuild. If you can pull the codes and reply back, I will see if I can steer you in the right direction from there.