They'll have to change the fluid seeing as they need to drain it when the DS comes out. Unless they catch it and put it back in... that would be fine for fluid you know is fresh but not old fluid...
For an 03, give them 3.2 quarts of Pennzoil Synchromesh to put in. Avoid any Royal Purple products like the plague and also any synthetic trans fluids. 3650s do not do well with full syn trans fluid. I have Synchromesh in my 3650 and it shifts damn near as well as my fresh T-5 did in my old 5.0 and a million times better than the TKO I had a few years ago...