My way for changing the duramax oil is to fill close to the proper amount and wait a couple of days or more to check if more is needed. Hard to see on the dip stick with clear oil also the big oil cooler makes almost 12 qts of Rotella synthetic T-6 oil. It is done in the summer but don't drive it from late April until the trip south. My bones feel the concrete floor in the garage more each summer. Replace the rear diff also as I do every other year. Fuel filter is a stand up job. My thinking is it's the right to treat his truck as he or she wants to do.
chevman