I'm still new to owning a diesel truck so any advice would be helpful. 2002 F350 Crew cab short bed with 215,000 miles on it. It runs like a champ but I have no idea when the tranny was last serviced. What should I do with it? I am planning on buying a 5th wheel so its going to be pulling some heavy weight but I do a good amount of city and cross country highway driving. I have a DP-Tuner and it shifts pretty nicely now but reliability is a big deal for me. Should I pay to take it to a transmission shop and have them flush it, or can I do that myself??