2012 ram 3500 6.7 cummins HO. and 3.42 gearing, all the smog stuff intact.
I get 19-20mpg on hwy empty,(1650rpm at 60mph)
Towing my 34.5 TT 9000lb, 11mpg at 60mph. on the flat prairies. in the mountains I drop down to 9mph very easily.
I have 4500miles on the TV, right now,this rig is matching my mpg of my previous 06 2500 with the 5.9l, and 3.73's (towing). I know the gearing is making all the difference in the world for this combo.
I think 10 mpg for your setup is very good,(very nice setup BTW) maybe run the premium fuel, keep your speed down, and it might get a little better but not much.
The best mpg will be with a turbocharged diesel tow vehicle and a truly aerodynamic, comparatively low weight aluminum travel trailer. A question of horsepower demand . . the less power needed to pull the TT at highway speeds, the lower the power required of the TV, thus a smaller TV as well.
MPG is mainly small stuff (past travel speed). Do all book maintenance and do not assume that TT axle alignment, wheel balance or brake drag is acceptable until confirmed. Same for hitch rigging: use the scales per the formula to be found around here. TV also needs to eliminate any steering wander or incorrect tire pressure issues (past brake drag & alignment).
Know your stops in advance. Use cruise control as much as possible. Break up the day of travel into segments that allow the driver to not become stiff (as mpg is also driver alertness. We use two hour stretches in big truck trip planning, about 100-miles. Get out and move around. Plan food and fuel stops consistent with this.