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Message: [QUOTE="TD-5, post: 1184740, member: 12311"] With 4.56 it will pull like a freight train, but 2400 rpm on the highway for hours at a time is going to consume fuel like a freight train too. 4.30 wouldn't disappoint either, they just won't pull quite as hard out of the hole, but these engines have so much torque the bottom end pull won't feel much different, One think to remember, Ford dropped the factory gearing in 2010 to 3.55 with optional 331 to try & improve fuel consumption at highway cruising speeds. These things like to burn fuel at higher RPMs Running 4.56 with your 37.7" tire is the equivalent of 4.11 with a 275/65/20 (34") tire. This would be similar to a F350 dually with 4.10's Running 4.30 with your 37.7" tire is the equivalent of 3.87 with the same 34" tire. Being your truck is an 2008 it most likely has 3.73 factory gearing, so the 4.30/tire combo would give you a slightly deeper equivalent ratio than what your truck came with from the factory in stock trim. Either gear ratio would be fine with your tire. [I]"(70x(4.30x.71)x336)/37.7 = 2045 @ 70mph"[/I] this is actually 1905 RPM [/QUOTE]

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