So i'm going to do a gear swap to my '02 FX4 screw here in a few weeks. I'm running some 285/70/17 Pro-comp All-terrains (about 33" tall tire), 6" Fabtech suspension lift with the current stock 3.55 gear's.
My gas mileage is horrible at 11 to 12mpg around town (over-drive off, or on, doesn't matter it still sucks). Highway mileage is about 12.5 mpg. The area i live in is Very hilly since i live in the valley between 2 mountains. Going up a small grade under 65mph, the truck has to down-shift out of OverDrive to get up the hill without slowing down. I pull a 6x12 enclosed trailer (2,000lbs max) and will probably end up pulling a 7x14 enclosed trailer as well (3,500lbs max), Highway speeds around here are 70mph and I routinely use them and slightly over when pulling the trailer.

I thought i had my mind made up to go with 4.56's as I plan to run 35" tall tires sometime (no sooner than 2 or 3 years). But reading through some threads, it appears this may be to much gear for my current 33's.

Waiting to re-gear is not an option as I really need to take the strain off the trans, and upgrading to 35's isn't either right now.

So, should I go with 4.10's or just keep with my decision of 4.56's?

80% of my driving is City driving, with towing happening every weekend between march and november (about 20 miles one way), with a monthly road trip of 400 to 1000 miles round trip.

Suggestions,comments?

 

if you eventually plan on getting 35s then get the 4.56s hands down.. buddy of mine ran 4.56s in his leveled f150 for a while till he got it lifted since he was in college.. and lift/gears/rims/tires couldnt all come at once lol.. definetly go with the 4.56s man

 

Make sure you also get a programmer so you can load tunes and correct your speedometer/odometer for the non-stock gears and tires.

If you have a 5.4, with a programmer and custom tunes you could get by with 4.10's, even with 35's.

 

I would go 4.56. While tire diameter is a big factor in choosing gears, think about the added weight of those tires/wheels, increased air resistance from the lift, and towing on top of that. Guys with lowered trucks run 4.10 with tires smaller than 32-33", and their tire/wheel combo is generally lighter than yours. Their trucks are also stock height or lower. Just food for thought. Post back after the swap!

 

I say 4.56s. Since you do mostly city driving and towing you'll love the deeper gears

 

x4. 4.56's on my truck, 35's in the summer, 285-75-17's for the winter. Truck feels great with new gears. I had 3.55's and would never go back.