oh sorry!! Drain back as in fluid draining back into the trans from the torqe converter, it happens slowly, and the longer it sits there with no pan on the more fluid you will have to replace. I just changed my filter and adjusted the bands the other day, so mine was off for a while, ended up putting in about 6 quarts to get it back were it needed to be.
With a free flowing exhaust and the silencer ringMIA on my 2000, you can hear the turbo winding down real well, ive had a couple people ask me whats wrong with my truck!!