Wow might have to start making some noise myself. If I get anything heavier than 30k my mpg goes to crap. Not to mention I had her less than a month and already had to put her in the shop twice. Lost a couple of good loads because of it.

Quite a bit of it is technique. Just sitting back and letting the cruise control handle things will eat a lot of fuel - its great on the straight and level, but it can't anticipate a hill and it only knows to apply full throttle once the truck is below the set speed. In hills, you can do better on the pedal. Limiting your turbo boost in mountains, downshifting earlier than just leaving your foot in it, will all contribute to better fuel mileage.

The way I learned how to do it was I got a spiral notebook. I logged the fuel used and fuel economy for every trip, and broke down those trips into legs - usually between places I stopped for a break. What you do is get creative about how you drive - and see if any of it contributes to better fuel economy. Change one habit or technique at a time, so you know whether it works or not, and do it for a couple of weeks so you can average out other effects. Over time you'll see what works and what doesn't.

But it starts with writing it down, and keeping track of your fuel economy - religously!

Here's a start: It matters how you distribute weight between the drives and tandems. Getting close to equal is helpful, but if you have a choice, put more on the drives - not more than 500 or 1,000 lbs. Tail-heavy loads eat a lot more fuel than nose-heavy ones.

Take it easy on the throttle... you don't have to floor it to get up to highway speed.

Don't accelerate up hills... hold what you have, and let gravity help out.

Don't let the cruise control accellerate you downhill.