The plan for my tow vehicle
 

I bought a 93 dually automatic to tow my 38' 5th wheel back and forth between Eustis, FL and Florence, AL Most towing will be relatively flat, but there are some pretty steep grades north of Birmingham. My 518 and rear end have had recent rebuilds and the brakes have been gone through. My plan is to add a 366 spring while resealing the pump, replace the 18cm hot side with a 16, and add an M&H dynamic spacer to the pump. I'm trying to help the motor a bit without cooking it. I sold my Banks equipped 03 quad cab dually less than a year ago and bought a GMC Canyon after selling my Arctic Fox camper, but when I decided to move back to Alabama I found I still needed diesel power. I bought this one for two grand and it has a strong engine. Body looks like warmed over garbage, but that doesn't matter!
Any suggestions or critiques?

I haul rvs all over the US and the best thing I did for the money was added a propane injection setup.
A good hp and mpg improvement plus the oil stays cleaner and egts are lower. On my 92 with a 518 and the pump bumped I got a 4 to 5 mpg improvement empty and 2 to 3 loaded with campers up to 12,500 lbs.
I'm still working out my 92 with a 5spd I just picked up, I just made my first run with a sock pump setup and got the same improvement. We will see on the next run after I take care of the pump.

Thanks; what propane injection system are you using?
And what hitch are you using?

I'm using a reese 15k 5th wheel and a frame mounted custom receiver hitch.
The kit it listed on Ebay Item number: 180801553688
Item location: Manitowoc, WI, United States.

How much propane do you use per tank of diesel? I would like to know what your mpg improvement would be if you added that propane consumed into the equation.