I tow a lot! If you live in the flat country then go 3.73. If you are going to put 35's on then 4.10's and you can still tow fairly well. If you live in the mountains then keep the 4.10's and just slow down on the highway. After all is said and done you need to decide what your truck is used mostly for and set it up for that reason. Drive at 60-65 and get 20-21mpg at 70-75 I get 17-18. If I am towing at a safe same speed you know 60-65 I get 14 or so. After all it is a truck no a street racer
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2005 3500 4X4 Quad Cab Laramie DRW, 5.9 CTD, G56 trans, 4:10 Detroit Locked, Amsoil, Rancho 9000, Tailgate spoiler