I would imagine you drain it with the engine off. Don't want it running when there isn't any fluid in the tranny! Only have the engine running when filling the tranny back up (i.e. fill it as much as you can with the engine off, then start it, cycle the gears slowly, wait until warm and fill as needed). As for which fluid is better, I was kind of wondering that myself. My Explorer has 69K and I've been thinking it might be time to change (or at least check) the fluid. I haven't checked it yet as I bought it only a few months ago (supposedly the dealership checked the level during their pre-sale inspection, but who knows if they really did).