I'm interested in changing my auto trans fluid, however I'm not interested in doing a trans flush. I figure I'll drain out the few quarts in the pan, fill, and drive a bit and then repeat. By the end of the week I'll have "mostly" new trans fluid. My specific question is when I drain the pan, would it be beneficial to then put the plug back in, start the truck, run it through all the gears and shut off. Would there be more fluid in the pan to drain, and would that procedure harm the trans?