flatlander_summit

I am shopping for new Ecos and am wondering what you guys are running for rear ends. 90% of my driving is city/highway mix empty with about 10% pulling a 18 ft. boat, 2 place enclosed snowmobile trailer, or a lightly loaded car trailler. Any heavy duty pulling will be done with a 6.7 stroker.

I know I don't need the 3:73s but is there a big difference between the 3:31 and 3:55 rear ends for the light pulling I plan on doing? Is there a big mileage dfference between the 2 higher speed rear ends? Any advice from you guys is appreciated!

Toddman38

iTrader: (5)

I have the 3:31 rear end, but I don't tow a damn thing in my 2012 xlt 4x4, and I like it! You should be fine if light towing is all you'll do... Higher gears will tow heavy loads better, but also reduce your fuel economy as well!

Toddman38

iTrader: (5)

I say test drive the two 3:31 and 3:55, you probably wont notice any if much difference...

Combat vet

I have a 5.0 Screw 4x4 with 3:73 gearing. Off the line power is strong and mileage is very good. Best highway is 21.3 with an average of 18.6. If I make short drives in the city, mileage varies between 14 to 15.5 mpg. I have always preferred 3:73 or 4:10 gearing for max power, especially when towing. With the 6-spd transmission, cruising rpm is not excessive, if I remember correctly at 70 mph my rpm is about 1600. Another plus: on resale, 3:73's have always been a positive selling point.

yokev

I test drove the 3.55 and 3.73s, and there was a few hundred rpm difference cruising at 75mph on the freeway. Before I bought my Eboost, I nabbed people driving on the road, in gas stations, and one guy that was pulled off on the side of the road smoking(a doobie) and asked what they're average MPG is. 3 with 3.55s and 3 w/3.73's, and to a MAN, they all said '15mpg'. Curiously 2 of 'em were 2wd, and yet they reported the same mileage as the guys with 4wd.
One thing to consider that not many people do, is if you're planning on leveling it out and going with 33's or 34's, definitely get 3.73s. If you're planning on running 35s or larger, you'll wanna swap out to an-above 4.00 ratio(obviously depending on what size you end up with) anyway, so what you get stock won't matter.

smurfs_of_war

I've been happy with the 3.55's in mine- it seems to be a really good balance between workhorse and highway. 3.31's might be a bit anemic if you really load them down, but I can't speak from experience on them- I suppose with enough torque any gear ratio will tow. I just wasn't going to chance that because when I load, I load heavy, but I also do a lot of highway driving. 3.73's crossed my mind, but I took the middle road on it. Right now I average about 18-21 MPG highway with a 5.4, I have hauled more than double the payload rating in the bed, and pulled a couple monster full trailers without issue, and pulled strong. No TT's yet- but that's soon . I don't even bother to calculate the city driving.

kydsid

My 2010 had 3.55's as this gave me the same final drive ratio I was so familiar with in the 4 spd/3.73 I had in the previous generation. It also had the 4.6 3v and it served me well towing anything I put at it but I that was all just loaded utility trailers, a few cars and a uhaul trailer or two. Lifetime average for the truck was 18mpg unloaded to 11mpg while towing.

When I bought the 2013 I drove the 5.0 with all of the gear sets. To me 3.31 with the 5.0, at least maybe it was just the trucks, but among those three the one with the 3.31 was the smoothest. So now I'm in a 3.31, but I haven't towed anything with it yet. At 17.1 mpg all city and rush hour highway driving and still going up. I expect to easily top 18 easily , maybe even 19 once I put some nice mellow non stop and go highway miles on the truck. I also made the choice since I'm like you 10% towing and the ability to go get the diesel if the little truck can't handle somethin.

CDC5.0

I have 3.31 gears in my 5.0 Scab and I love them. Power is still awesome and highway mileage is great, I've seen as high as 23mpg on long trips. The gearing in the 6 speed transmission really helps the engine dig deep off the line regardless of what rear end you have. But if you want the best towing capability and off the line punch, then 3.73 gears is the way to go.

Combat vet

More info to help you (or anyone) decide which rear axle ratio to choose.

In addition to changing the direction of power flow by 90 degrees (from the driveshaft to the axles), the purpose of the rearend gears is to multiply the torque delivered by the engine and transmission. Gears can be thought of as complex levers. In other words, they provide a mechanical advantage that multiplies work-in this case, torque-to help the engine's power move the vehicle. Lower gears are like a longer lever: They provide more mechanical advantage. Higher gears are like a shorter lever: They provide less mechanical advantage. It's similar to when you use a long breaker bar instead of a short ratchet handle to remove tight lug nuts. Just like a long bar puts more torque on a lug nut, lower axle gears provide more torque to the wheels.

Read more: http://www.carcraft.com/techarticles...#ixzz2ENrXOUt4

kmac1036

I got the 3.55 in my truck (3v 4.6) & it does ok. I pulled a 14' cargo trailer loaded with furniture. I only got 9.6mpg. the truck would go faster than 65 but was running 3k+ on the tach. settled down around 62-64 & was running around 2k rpm. has a tenancy to downshift on grades & such. that was my only complaint was a bit tough to keep it in OD.