I am towing right at 10K with a 2012 F250 6.2. I only look at the puter when checking gas mileage for the hey of it. On a run from Myrtle Beach thru the Smokies and to central IL it consistently knocks out 8.7. I tow at 65 on the flat. It has the 4.30 diffy.
I do not know what folks are talking about when it comes to mountains. Around the Saluda area in NC going north on I 26 there is a long 6% grade. I topped that thing at 45 mph with the old 99 psd. With the 6.2 (I don't hammer down) I can top it easily at 45 and could go faster if I put more pressure on the go pedal.
With that diffy, I am hard pressed to knock out 14 when empty and cruising at 75.
I looked at the puter yesterday. Have been spending all the time on short trips and in town and it showed 13.2.
I have been happier than a pig in slop with my switch from the old rattler to the gasser.
Now to get right down to the legend of towing in the mountains. Aren't interstates graded at 6%?
Feel free to PM me for any additional questions you may have.