I experience the same gear/rpm that the OP does. 2010 screw 5.4 3.55. I sure wish I could lock out 6th gear though. I hit 6th sometimes, but not for long. Definitely not long enough for it to be worth the extra shifting. I never go over 65mph either. Love the factory TBC and sway, but I do also use a WDH with sway control bar. I get 8-10mpg pulling 24' TT, about 5k pounds. Pulls like a dream

Empty mpg is 17 city and 22 highway.

 

Wow! I wasn't even close to those!

 

2wd at 65 mph and a tonneau cover. I'm a tightwad.

 

Ditto. 2WD and tonneau cover for me too, but I have 3.73's, tow mirrors, and a bug guard on the hood. So I get 17 city & 19-21 highway.

 

Still not bad. I like the 3.55's when I'm empty, but 3.73's would be nice when towing. I think I turn about 1700 rpm at 65 mph

 

I'd install 4.10's or even 4.56's if I could find a good shop. The truck's #1 purpose in life is towing the TT on family trips. I didn't buy it for fuel economy. Besides, the double overdrive tranny would still keep RPMs reasonable.

 

If I didn't drive so much while empty, I would go with 4.10's as well. last truck was a power stroke with 4.10's and I loved it, but it was close to 20 years old with almost 500k miles. Not a good daily driver. I wish I could afford two trucks!!!!

 

Oh yeah!