A lot of people (including myself) change out the factory lubricants in the motor and the differentials early, within the first 2000 miles or so. I did this on my last truck, and included the manual transmission. My new truck has one of those "sealed" automatics that are supposed to be good for 100k miles. Aside from getting into an argument with a dealer about whether it's necessary, do you recommend doing an early flush on the transmission, or leave it alone? I don't know what a full transmission service costs, so I don't know what is involved.