The 6.6 transmission is tied to an overdrive transmission so final drive is very different from your 7.3. You can also manually shift with this transmission too. Ford's towing specs says either will work with that load. That said, if you are or expect to be towing in the mountains, or will be towing that load on the flats 75% of the time versus running empty, I would try to change the order; otherwiosee should be fine. If mainly running with light loads stick with what you ordered and your mileage will be better.

 

3.31's will tow that all day and not even break a sweat. You gotta think too, you're going from 525ish ft. lbs. of torque to 800 ft. lbs.

 

The 7.3 had 525 lbft of torque at the crankshaft, here is the axle torque in the various gears of the 4r100 with the 3.73 diff vs the new powerstroke with 800 ftlbs of torque and 3.31 gears:

..............................................7.3 liter........................6.7 liter
rear axle torque in 1st............5300 lbft .................... 10,512 lbft
............................2nd...........3016.......................... 6,143
............................3rd...........1958.......................... 4,024
............................4th............1390......................... 3,045
............................5th............ n/a.......................... 2,277
............................6th............ n/a.......................... 1,774

These values are only for comparison purposes as they assume no torque loss in drive train. The 6.7 with the 6 speed has so much more torque that even with the 3.31 rear end you will be thrilled if you're comparing to a 7.3.

 

I would say that 85% of the time I will be running empty or towing in the deep south. I do make a yearly camping trip to the Smokey Mountains and eventually I would like to go out west. I guess I could live with it since it's probably too late to change my order and I don't want to wait an extra 3 weeks for it to come in. I guess the extra 275 lbft of torque should make up for the gear difference. Thanks for the replies.

 

You won't even know it's back there.:thumb:

 

I also went from a 7.3 (3.73 ratio) towing a 11000 pound 5th wheel and a horses trailer weighing around 8000 to 9000 pounds depending on how many horses loaded. I have towed the horse trailer around 10 times this spring and with tow haul it is a pleasure. You cannot really tell that the truck is working at all. I am very happy with the 331 ratio. Fairly soon We will start using the 5th wheel and I am confident it will do it well with the 3.31 gears. I really like the exhaust brake so far.

 

The 3.31 is a whole different animal! I tow a 12,500 lb, 33ft trailer and most of the time forget it's even there except for when I see it in the mirror.

 

8upbowhunter,
For the uses you describe I would not change the order- even if there were no time delay.

 

My toy hauler wieghs about the same empty 37' 11500lbs cant even tell its there. I pulled my buddies 40' its 16k empty to vegas still had plenty of power the differents is in the fuel mileage it cut in about half. I also have the 3:31 and on top of that have 35" tires so I wouldnt worry about. Enjoy your new truck:icon_ford:

 

With 6 different gears to choose from, the tranny will stay locked in one of them no matter what. I have 3.55's on mine and it will stay locked in 6th pulling 7500 up 7% so I'd imagine the 3.31's are similar.

 

Where is "Tim, the tool man, taylor" when you need him. The testosterone surge is palpable.

 

I think it will work out with these gears. Only 3-5 more weeks to wait now.

 

Our TT is only 8,500 - 9,000 lbs but there is enough power, even with my 35" MT's, that I would feel confident passing up a grade. And I have yet to be upset at my truck for downshifting. So much better than towing with a gas truck.

 

Our TT is only 8,500 - 9,000 lbs but there is enough power, even with my 35" MT's, that I would feel confident passing up a grade. And I have yet to be upset at my truck for downshifting. So much better than towing with a gas truck.

Your right about towing with a gas truck. That's what made me buy my 2001 F-250 7.3L PSD 10 years ago.

 

ShirtaDay, are you running Hankook MT 35x12.50R18's? Looks like they are on your stock rims. Do you have a lift or leveling kit? Do they rub when you turn? Thanks for your help.

 

Precisely. Yes. Nope. Not at all.

So far I'm very happy with them. I run Hankook's on the wife's H3 mounted on the stock 16's. Those have 20k miles and look good. Mine have maybe 10k?

 

It crazy what these trucks can do! Just a few years ago 3.31s were pushing it in a 1/2 ton, and unheard of in 3/4 and 1 tons. Now you can have the towing power and get decent mileage! Amazing! :woot: