Either the TST PowerMax-CR or the Smarty will add timing and I have found 1-2 mpg from either of them. I believe Edge is also making a box to add timing. Stage 1 injectors like DDP will help 1-2 mpg, as will fresh injector bodies if there are a lot of miles on the truck (say, over 100,000). Beyond those modifications are the “obvious” things—use stock size tires and no lift kit for minimal wind resistance, don't carry more weight than necessary, optimize driving habits, and lower your rate of acceleration and your road speed (say, 65-72 mph rather than 75-up). The six-speed transmission will be the New Venture 5600 with iron case.