Super 10 to RTOO swap

I have a '99 379 with a 3406E and a Stupid 10 behind it. Rear gears are 390's. NOT a good mileage or high speed combination. I plan on returning to the Oilfields when the price of oil goes back up so I wish to retain the 46,000lb axles and the 390 gears. With that said, I am on the road for as long as it takes, and even though fuel is reasonably priced, 65mph at 1500rpm is not great. At 75mph I'm running 1850rpm. I believe than a 13-"double over" will be the solution I am seeking. Has anyone done this swap recently? What are the torque specs for a RTOO11613 or a RTOO14613?? with the stupid 10 the torque is low being that the Super-10 tranny is a turd. Any help would be great! Thank you

 

From what I have researched it should be a RT0011613 or an RT0014613. I spent 10yrs working in Western Colorado, the Front Range of Colorado, 5 winters in NoDak and some time down in the Eagleford Shale of Texas. AT LEAST another 2-3yrs is what I am expecting.

 

4.2mpg is about the best I can muster out of this pig, these older Cats are higher rpm than the C-15. I've driven at 65mph for 400 gal of fuel and then 75mph at 1850rpm across Nebraska and Wyoming with even worse fuel mileage. Something has to give. To change the pinion gears in both diffs will cost the same as a transmission, I have to do something.

 

What is your average with the 15? Are you running a 15 over?

 

It sounds to me as though my best bet is to bench these 390's and go with 330 or 355's. They aren't much for a set of remanufactured differentials and I'm going back to an 18spd, these 10spd turds are entirely too much shifting back and forth, too low of rpm then too much rpm.