Thank you for all the helpful replies. My truck does have the 6.0L gas engine with a 3.73 rear end. The mileage with 2,300 miles on it is 12 - 12.5 in city driving. I tow a 3500# - 4000# landscape/lawn mowing trailer with equipment and get about 11.5 - 12mpg. I did take it on a highway trip for about 250 miles and got around 16mpg. I did change the oil at 2178 miles and then sent it in for oil analysis. I was planning on doing the oil change once a year since my truck falls into the severe service for the 0w30 motor oil and also oil analysis each year. I am also on planning on changing the transmission and tranfer case oil at around 3,000 - 5,000 miles to the Amsoil ATF. Then change the differentals at 3,000 - 5,000 miles to Amsoil severe gear oil. I am also thinking about installing a bypass system but not sure if it would be worth it or not. Most of my driving is less than 10 miles one way. I usually put 10,000 miles on a vehicle a year with 3,000 is usually lawn/landscape business miles. I just spent a lot of money on this truck and I plan to keep it for 10 years. I rely on it for a daily driver and business, so I really wanted to take care of it.