I mostly let is stay in drive and toggled OD on and off when needed, though different tracks require different driving styles. At VIR South course there are the Downhill esses, quick, off camber, down hill esses. Very fun, but for me to take them with confidence, I was pulling down in to second where i could maintain a quick pace but without jumping into third which would have been too fast and since south course is so hard on brakes, it was an area I could cool them off by using engine braking ILO pedal braking.
You really shouldn't pull down but you really shouldn't track a truck either. I never had any tranny woes other tahn frying the fluid once or twice on my favorite course. 11 miles AutoX, 318 curves, very sweet but not uber fast ~70mph was about all you really needed, there was only two spot where I would pop into third for about 300yds or so, but right back into second, where I could use engine brake and not out speed the corners too much. I know it sounds like a wussie driving but trust me, I mode more people puke than anyone else on that course.
Bryan