Brambo_atx

I have owned an 01, 02 and 05 4x4 screw and currently have an 09 King Ranch 4x4 screw. I have a 3.55 rear end in it and the 5.4 V8 and it struggles up hills, but pulls fine on flat ground. I have a 21 ft ski boat that I pull on weekends. Otherwise I run empty and have a 25 mile commute to work each way. I am looking at ordering a 2012 King Ranch 4x4 screw with the Ecoboost engine, but not sure which rear end to get. Any advice?

dejong1

3.73. I have it in my 5.4 and love it

jdgray511

I have an Eco with 3.73's n it pulls great.

lddrew

3.73 if you pull a decent amount and it is of significant weight

76736

+1

69428SCJ

I would go with the 3.73's as well. I tow a 25' Baja with mine and it rarely hunts for a gear. I believe that is the only ratio that the ELocker is available with as well. Fuel mileage empty is going to be a just about a wash.

Brambo_atx

Thanks. I was wondering if the mileage difference when empty was big between the two. If it isn't much, I'll order the 3.73 since the main reason for the new truck is better towing with the boat ( and hopefully better empty mileage).

zx12-iowa

i have eco 4x4 w/ 3.55 and pull 6k lb boat. pulls great and never hunts. pulls way better than my 5.4 w/ 3.73. empty w/ cc set at 65 i get 22 mpg consistently. you will lose 1 mpg or so w/ 3.73 but it will pull a tad better. with the weight you will pull you dont need it.

Kenneth Forbus

It is all about what you are looking for... I have 3.55 rear end in a SCrew XLT 4x4 and never have thought my ecoboost was under powered. It has tons of power! The torque is amazing and so love pulling hills without dropping gears. Plus when I consistently knock down 20 mpg on a tank of fuel I jump for joy. A good friend bought a FX4 ecoboost the same day as me and has a hard time getting above 17 mpg which I mostly attribute to gearing. I pull a 3.5k bass boat on a weekly basis with no issues; so unless you own a 9k trailer go with fuel economy and let that ecomotor do it's magic.

Mike Up

WOW, if you're struggling up hills with the 5.4L, you should change your air filter. I had a plugged air filter and it definitely robs a lot of power besides giving you really crappy mileage.

I pull my 23' 5000 lbs high and wide profile travel trailer (in sig pic) up hills/mountains and have pulled in 50 mile/hour winds and have yet to see it ever struggle. I'm impressed with it's power everytime I tow. I also have the 3.55 axle and it has a great over all ratio in every gear. Only the new Chevy motors with the 6 speed trans and the Ford motors with the 6 speed trans, offer better overall ratios with the 3.73 than the 3.55 axles. Besides Chevy and Ford 6 speed/ 3.73 combos, the Ford 6 speed/3.55 combo offers the best overall ratio out of all makes. It has the best pulling gears. The 3.73 allows the Chevys and Fords to pull over 10,500 lbs while the others are under 10K in a Crew Cab 4WD configuration.

I love the 3.55 plus I get about 2 mpg better mileage than what others are reporting with the 3.73 gearing in the same configuration truck.

If I didn't care about mileage and didn't want my limited slip differential, then the new 3.73 locker would be my choice. The 3.73LS was offered with the Max Tow package but it's very rare around here to find an XLT max tow, most are Lariats that I didn't want.