fuel tank

Why not just replace your tank with a bigger one? http://www.aerotanks.com/vehicles/chevy.html

Might be a problem, might not, but be sure to consider the additional weight of the tank and fuel.

Not sure which model might work for you, but I bought the RDS brand (42 gal tank/tool box combo) some years back. At the time, I wasn't sure if I was just splurging on an unnecessary investment. Now, I can't imagine living without it. I am very happy with the RDS brand. I installed it myself just going by the instructions and it has worked flawlessly. Northern Tool had the best price online, shipping was a breeze, and I saved over local vendors who wanted more and charged sales tax. Good luck.

My dad picked up a combo tool/fuel box from http://www.thefuelbox.com/. His the FTC60. He got the optional plumb it in to your filler neck option. Works great. As the level gets a little below half tank on the truck, the auto-controller fills the truck tank back to about 3/4 full, and continues the cycle until the aux tank is empty. The aux tank level is displayed on the little control box. It requires tapping in to the truck's fuel tank sending unit (easily found in the wire loom running along the frame rail).

The spray on bed liner type coating is nice as well. There are other cheaper cost aux tanks out there. This one is an expensive purchase, but money well spent.