I dont want to sound harsh, BUT dialy driving 6 miles to work is a gross missapplication of the vehicle. Any of the diesel trucks are really ment to work hard at towing, this is where they shine. I have seen many of the 6. 7s that tow HARD and none of them have had short oil change intervals. Being a CPA and doing the math on this I would think that you would find a little Toyota that would get 35mpg and only need 3 quarts of engine oil every 4000 miles...