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Old 07-29-2021, 09:16 AM   #21
Dan Lockwood
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Join Date: Sep 2019
Location: O'Fallon
Posts: 209
I have a three month old '21 F-350 King Ranch dually 6.7L with the 3.55:1 able ratio...👍

I was REALLY hoping for a steeper gear, 3.73 or even a 4.10 based on my '12 RAM 6.7L dually with a 3.73. But the 3.55 is doing a GREAT job!

The Lie-o-Meter says on long unloaded trips in just over 19 mpg and towing at 70 mph I'm at around 9 mpg and at 60 mph I'm around 10.2 mpg. Around town normal daily driving I'm in the mid teens. I checked two tanks actual compared to the truck computer and the truck was about .3 optimistic...😀 Your mileage may vary.

My rig is on the heavy side, maxing out at 18k# triple axle. I can excelerate to 70 mph on freeway entrance ramp ready to merge smoothly when I hit the freeway. Once I'm on the freeway I'll adjust my speed. 👍 I could not do that with the RAM, not even close. But almost 200 hp and 250 torque more, things happen a lot quicker.

I really don't think you can go wrong with the standard 3.55 ratio.

Mine is not an electric locker, but I know when I lit the tires up in front of my neighbor's driveway, I left four black marks. I was empty and only did about a foot in length, but I just had to do it...👍 As they used to say "the Devil made me do it..." 😀

Good luck with your new '22!

PS: Forgot to mention the 10-speed transmission. This transmission is the greatest thing since sliced bread... Don't let the low 3.55 ratio fool you, this will keep you always in your power band.

The first gear is 4.7:1 and believe me, it gets things moving very fast and smoothly. Just about like the granny/creeper gears in the old 4-speed manual truck transmissions. I'm very happy with how it performs...

First - - - - 4.696:1
Second - - 2.985:1
Third - - - 2.146:1
Fourth - - - 1.769:1
Fifth - - - - 1.520:1
Sixth - - - - 1.275:1
Seventh - - 1.000:1
Eighth - - - 0.854:1
Ninth - - - - 0.689:1
Tenth - - - - 0.636:1
Reverse - - - 4.866:1
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Old 07-29-2021, 09:33 AM   #22
Join Date: Aug 2012
Location: alabama
Posts: 34
If you are going stay with stock tire size 3.73 is a great gear for towing. I have them in my ram dually and have no issues with my combined weight of 26,000lbs
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Old 08-24-2021, 12:48 PM   #23
Join Date: Sep 2014
Location: Southbend Ar.
Posts: 78
Stock tires, 373 gears, 10 speed
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Old 08-24-2021, 01:07 PM   #24
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Originally Posted by wesaysoracing View Post
Stock tires, 373 gears, 10 speed
If that's a gas engine, hitch a trailer behind the truck and the mileage goes to half????

If it's a diesel, when in "regen" the mileage goes to 12 or hitch a trailer and it goes to 11... Trailer AND regen ??? We won't talk about the MPG for those few miles

Running "solo" at 68MPH in ideal conditions in "second overdrive" at 1600RPM with a tailwind" is typical of most newer trucks these days.

When they're "working" though.... well, that's a different MPG reading "fer sure"...

2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS
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Old 08-24-2021, 06:03 PM   #25
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Join Date: Mar 2021
Location: Owosso
Posts: 189
Funny, DW and I headed north to a new campground on Sunday. Watched the Lie O Meter and we’re getting 9.2-9.3 out of a a truck that is a rock solid 10.2-11.5 with my rig. Get settled in and go for a drive. I’m still like wtf is up with the mileage. We get back and I smell diesel..strongly. I’d smelled a whiff twice earlier but didn’t give it much thought. Now I look underneath and see diesel dripping off the frame. Oh s***. Lift the hood and there is diesel on topside fuel filter housing. Call the local Ford dealer (Mike Lynch Ford, Rogers City Michigan) and they say bring it in. Great folks. Had a failure on my topside fuel filter where the casting hole for the plastic “blew out” for lack of a better term. Was shooting a toothpick diameter of fuel out the top about three inches. They had the part and had me back on the road in under an hour. Kudos to them and a huge thank you. Just wondering how many gallons I urinated out on that almost four hour trip on US27 and I75. Needless to say, mileage is back where I expect. I wish my truck hit 19mpg. Wow.
Joe & Mary
2015 F350 XLT CCLB SRW 6.7 PS
2018 Cougar 344MKS
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Old 08-27-2021, 05:52 AM   #26
Join Date: Sep 2014
Location: Southbend Ar.
Posts: 78
I was in 10th gear no wind, 7.3 gas, empty
towing 5th wheel 8.1 mpg The truck preferred ninth gear about 1800 RPM
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Old 08-27-2021, 08:45 AM   #27
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Location: Germantown, TN
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Joe rough figures give about 4 gallons dripping all over everything in sight. Smell won't go away for months.
Keep in mind when some RV'ers throw around 19 it can mean a lot of things: They are lying, they weren't towing, they had a 40 MPH tailwind, they were driving 45 MPHnot towing, they were lying....
Our F450, only comes delivered with 6.7 and 4:30 gears, just like all those who tell the truth, when towing, 8.8 to 10 MPG. Real figures, although our lie-o-meter is very accurate. Not towing, 2000 RPM, 65 MPH, 16.8 to 17.5. Just about average unless I were to get it chipped in which case the HP would increase to 750, torque to 1500 lb/ft and mileage up to 35. Okay, maybe the chipped part is campfire fodder.
Jim in Memphis, Wife of 51 years is Brenda
2019 F450 6.7 Powerstroke
2018 Mobile Suites 40RSSA
2021 40' Jayco Eagle
2001 Road king w/matching Harley sidecar
2021 Yamaha X2 Wolverine 1000
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