my 2001 crewcab 4x4 gets and has been getting for years approx20-21 MPG. I also am using 3.73 gears and have a heavy foot. The biggest factors in increasing my fuel milleage were the installation of pretty much everything banks has for this truck and switching all of my lubricants to amsoil synthetics. I also use a few items from www.dieselsite.com but I don't think there products had any role in my MPG. I've won many bets from people doubting this trucks MPG, in fact I can usually get better milleage with my 8000lbs loaded trailer than most get unloade. Maybe I'm just lucky, but I'll take lucky any day over 15 MPG. I had a fabtech 5.5" lift with 35-12.50R16.5's and didn't notice much if any loss in my MPG, probably due to the added power and the bigger tires not really working the engine any harder.