I can vouch for 3.55 gearset on 35s and a 3" level. Pulls my 16k trailer with ease. From a start your only delayed by the turbo which only takes about a half second to spool up. I DD mine and tow 75 mph with that 16k and it's right on the money where it should be, at least imo. I wouldn't want it any lower geared, turn too many rpm. I can always drop it to 5th if the need be for a long steep hill.

Turning a hair over 2k rpm at 75 mph and that's right on the money for DD and towing. It would piss me off for it to be turning significantly faster for maybe a little bit of off the line gain. I can only see 4.10s in duallys that are hauling most all their life.

Can you even get the 3.73 gearset for the 6.7 diesel? I don't think factory offers a replacement 3.73 for the 6.7, maybe aftermarket does...I would say if you found em 3.73 I would run if I were you...I wouldn't mind a 3.73 in mine.

 

Thanks. Yeah, Ford Dealer parts dept says the 373 from my '11 gasser is the same as the '16 diesel.

I am definitely going to make the swap as I lost 4 mpg going to 35"!!

 

with 6 inch lift and 35" going to 3.73 or 4.10, what in town mpg should you see?

 

I've decided on a 2" lift in the front only also known as a leveling kit. That leaves room for the 35" tires. This truck won't be doing aggressive off road like the last one!! I am going to try this with the stock 331 gears first. A friend of mine has a 2012 6.7 with 331 that has the leveling kit and 35" tires. He says his does just fine and pulls a bigger trailer than me. If I do feel a gear change is necessary I am going to put in 373 gears from my 2011 gasser when I changed it to 430. With the 35" tires it should be similar to a stock truck with 355 gears so I don't anticipate much of a mileage change.

 

My 2011 F350 had stock 3.55. I ran 35" and 37" tires just fine with the 3.55 gears (3.73 will def do you right). Didn't feel any problems towing or just street driving. I have since went a different route with the truck and turned it into a show truck and no longer tow. I went with 4.30 gears on 40"s and so wish I would have gone 4.56.

 

I would go 3.73's... I have 35's on 6 inches of lift with 3.73's and my stock 7.3 would tow with ease.. the 6.7 would perform even better

 

Thanks, I have pretty much decided on 373. Now the great thing about that is I saved the 373 out of my '11. Parts dept is checking to see if they will swap.

 

i run 3.31 pulling 15k plus with no problems.. What do you mean not impressed? Do you want to drag stop light to stop light towing heavy? Really, i remember pulling 15k with 200 hp and 300 ft lb torque with no problems.

I love all the power in my 6.7, but sometimes i wish they would cap this power for more reliability and way better fuel econo. Its getting crazy with power numbers now days, and people are still not happy. Drive a super-car or crotch rocket and quit towing..

 

Pulling the same trailer with my '11 6.2 with 430 gears was much stronger from a stop than the 6.7 with 331 which feels to struggle a bit. Once I get it moving there is no comparison!! Perhaps you missed the part where I going to lift it with larger tires which will knock the daylights out of a 331.

 

The "lower" ratio will be better for towing. As you stated the initial tug will be improved, but also the higher RPM at highway speed is also beneficial while towing to keep Temps lower.
Torque curve is flat on these trucks so it should push you into the horsepower a little more as well.

3.31s are for mileage and emissions. I have 3.73 in my drw 12 and it tows nicely. Given the choice I would have opted for 4.10, but she's not my daily driver either. The only reason I have this beast is to haul as much as possible and to tow. Not an economical commuter.

Also it seems that the stock shift strategy is to hold the highest gear possible, double overdrive pulling grade, at 35mph, and such is to low rpm imho.

Might be worth trying a tow tune and correcting for oversized wheels/tires before swapping gears?