Same Highway today, same outside Temperature as well @95F, running empty at 70 mph yielded 15.7 mpg as the computer stated (Hand-calculated 15.7). No complaints here, Should even do better once I get more miles on the engine.

 

Thanks for the update. Again, better than my 3.73's. I ran 100miles up the interstate and back, and just on that part of my drive, 70-75, I was right at 14. Then by the time I did my normal driving combined I ended up at 12 for the tank.

 

Dang it Rain. You gotta stop making me considering altering my order to the 4.3s just for highway driving reasons.

At this point I'm just banking on Ford getting the new transmission set up better for the 6.2. Hoping so...

 

Well, I did it. There seems to be enough data that the 4.30 gears just don't bog the truck down any at highway speeds, and can improve things around town. Going to alter my order to the 4.30. Should give me a little playing room if I want to run with bigger/heavier tire or level the truck out some.

 

Love my 4.30's so far PFG. I don't drive it aggressively but don't feel I need to, it has plenty of power.

 

That's cool you can still make changes. I got a Vin a week ago so I'm locked in.(color was my issue). I have been asking for weeks and weeks in the "ask an engineer" section for the gear ratio's of the new tranny. I don't think it will really matter as the final drive is still probably going to be in the .67 range.
I have said it before, but I hound my dealer about this stuff and it seems once the buyers go bigger than the 31.5" stockers, load the truck up, or tow, the potential gain of the 3.73 is gone.
I drove the wife's Pilot the other day down the hwy. I believe honda designs these things for mpgs and doesn't care about towing power and such. I noticed that at 60 the thing is running just over 2k rpms. Reminded me of the gearing ? on the SD gas. I am so used to the diesel trucks I have had, loving the 1200-1500 rpm range for hwy cruising that I never considered the rpm efficiency when I went to a gas SD. The modern day overhead cam motor is a high rpm motor and makes its power that way.
I fully expected to get at the top end of the mpg range when I got my XL 6.2. I carry no extra weight and scale at 6800lbs with fuel. I have added the modest 32.9" general at2's. My truck seems to just need a lot of pedal in 6th to keep it going down the hwy. Hard to explain but I can tell the difference vs when I drop into 5th and go from 1450 rpms to 1750. At that rpm the truck seems to more effortlessly move down the road.
I have yet to see a 4.30 truck that gets anything worse than me, and the ones I have seen do better.
I was thinking that at the 70-80mph range the 3.73 may be better but with the recent posts that doesn't seem to be the case. I gather that the increase in wind resistance far exceeds the difference in rpms as the major impact in mpgs.
If I can pick up power, towing ability and any mpgs, I'm all in.

 

Today I did about 65 miles of 75mph, the other miles around 120 were a mix of 55 to 65 and one section of 70 miles of mountain highway driving.
Computer stated 14.5mpg, hand calculated was 14.478 mpg.
The 65 mile section at 75 was at the end of the drive, this was the same tank of gas I was using with the 15.7mpg @ 70 which was all highway miles.
After top-off of Gas, the miles to empty is now stating 436 as the computer is now avg with the higher mpg running empty Vs the avg towing mpg.

 

I'm at 13.4 life time with 31,000 miles. I can get 15 if I keep my speed less than 75.