I have a 2002 F250 SC shortbed 4x4 that I recently put a 6" BDS Lift and a set of 315's on the truck. I have a 5.4 with 3.73's right now and I am going to upgrade the gears as soon as I can get some answers on gears, I have no idea about how geras are going to change the truck's performance, Just alot of here say.. I have been told that 4.56's will get me some of my gas mileage back because the truck is not working so hard and others are saying it is going to make it worse than it already is, I get about 9-10 after the kit was installed and tires were changed. I hope someone can she d little bit of input on this one for me. And I also have another question about the K&N Fuel Injection Performance Kits, Does anyone ou there have one on there truck, and if so Can they really feel the difference in power? I would hate to fork out the money on this cause they are a little expensive unless they work, Thanks again and i hope someone out there can help me out.

 

I am assuming you have the 265s on now? If so, you added about 3" in diameter to your tires, so translated, that's about 9% torque loss. A set of 4.10s will get you roughly back to factory. 4.56s will allow you to launch, but will cause you higher highway RPMs, which lead you to lower fuel economy, and may cause you to tow at slower speeds since you will now be out of your power band at the same highway speeds. If you're looking for better launches, but want to save some fuel, I think a good compromise would be a set of 4.30's.