2015 3.5eco FX4-4x4. with towing package, the one with sway control, the hookups on the bumper but no brake controller (yes i am installing the brake controller)
opinions on towing with the 3.31 E-locking rear?
i know it has less "off the line" acceleration than the 3.55 or 3.73, whereas i should have better highway MPG, my question is, opinions on towing with this set up
probably going to be getting a 28' class trailer, in the 5-7k lbs range.

and a side note, if the 3.31 is supposed to be slower off the line than a 3.73, then that 3.73 must be a neck snapper cuz this thing pulls like a sumbitch

 

Looking at the 2015 towing guide (https://www.fleet.ford.com/resources...Tgde_May19.pdf) it shows the 3.5EB with 3.31s and 3.55s to have the same GCWR (unless you step up to the max tow package). So Ford says they will both pull the same amount safely. The 3.31s might just need to downshift more or even be in a lower gear most of the time.

 

It's not going to be the most fun with 3.31s and the 6sp auto. It can do so (assuming all your other weights are within spec, payload, etc.). You'll want to figure on locking out 6th and probably 5th.

The 3.31s with the 10sp auto are a different story, as they work out to the equivalent of 3.73s on the 6sp auto.

 

 

ok guys, thanks for the advice

 

I've got 3.31s but on 34" tires (3.5EB 10spd) and I'm most likely going to regear. But I'm towing a 30' car trailer that when loaded is around 10K. When I've towed similar weights to your setup mine towed ok but a lower gear would be nice.

 

I suspect way too much attention is wasted on F-150 gear ratios, especially with the 3.5L EcoBoost engine.

My 2012 had 3.5L EcoBoost engine and 3.15 E-Locker axle, and I had no problem towing any trailer I wanted to tie onto. For one 300-mile trip through the Texas Hill Country, I towed a trailer that grossed 0ver 21,000 pounds (27,500 GCW) with no problems. Highway speed about 62 MPH using cruise control and tow/haul mode. I kept a close eye on tranny and engine temps, but it was a cool rainy day in early May so no problem of overheating the tranny or engine.

My 2019 has 3.55 E-Locker that was part of the Max Tow pkg. I haven't towed with it yet, but unloaded it feels sorta like a late-1960s muscle car, ready and raring to go. Have you ever driven a 1969 Hemi Charger with automagic tranny? If you press on the go pedal, you had better be ready to go.

 

3.31 gears 34" tires with 5* tow tune on the street.

 

I tow a 4000# travel trailer from 600' above sea level through New Mexico to Colorado and have never had an issue with my 2015 and 3.31 gears. Yes it does run in 5th a lot but I've never had problems going up any of the mountain passes, even Monarch pass at 11,300'.