f150fseries

This is my first post, although I have been creeping here since I got my first truck at 14, a 1986 f150, nice truck sadly gone now, I recently acquired a 2002 f150 7700 series for what I think was a good deal, drives great, took it on a 800 mile road trip no problem. I did know before hand the check engine light was on due to transmission related codes, really hope it isn't in need of a rebuild, I just wanted to know what transmission parts are serviceable, like if I drop the pan what parts can I replace? I want to replace what I can and then throw in new fluid, filter, gasket, and a bottle of Lucas transmission fix and hopefully fixes the problem. Thanks in advance for any help.