Question on 2008 Duramax Fuel Economy

[executivehauling]

Was curious if anyone knew of any good combos for the 08 Duramax's yet. I have a 2008 2500 HD 4X4 Duramax with the Allision Tranny. I love the truck and get close to 20 highway and 15 to 17 around town. No upgrades all stock. The tranny in this truck is awesome. I pull a 27 foot enclosed trailer with a v-nose. I get 13 when it is light or light loaded, and somewhere around 10 to 11 with a car of good size. This is highway driving too. I would like to get the most out of the truck for fuel mileage, and I would like to get one of the shift on the fly controllers, exhaust, and air intake. Bigger fuel cell, and toolbox combo. Any suggestions????