Got me beat. My city/highway average is 16 or 17 with a 4.3 with cold air intake, flowmaster, all synthetics, and the tb mod.
You need more torque. I suggest a 6.0.
2001 ECSB 4x4, 5.3, Radix, 3.0 pulley, VHP Trucker cam, 216/224 .551/.551 115 lsa, 1.8 Crane roller rockers, 4L65E, Yank SC3000, 3.73, Cal-Tracs, HPTuners.
Don't forget the s/c LS9 if money were no object.![]()
See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709
If money was no object I guess I could go with a twin turbo 572.... or just have two 4.3 engines in line with the 2nd in the bed. You have to admit that a sc 4.4 liter Northstar would be unique... and with 469 horsepower it would embarass just about any 5.3 or 6.0 I passed.
See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709