87 oct tune (Nelson) = .5 to 1 mpg increase
93 oct tune = 1 to 2 mpg increase
Air intake = 1 to 1.5 mpg
Cat-Back = .5 to 1 mpg
Electric fans = 1 to 2 mpg
Synthetic engine oil and sythetic trans fluid = .5 to 1 mpg
2-4 psi higher than recommended tire pressure .5 to .75 mpg
Lower rolling resistance tires such as a narrower tire and/or a street tread tire instead of an mud/snow tire == 1 to 2 mpg
VR velocity stack = 1 to 1.5 mpg (this is a what someone just reported on their Yukon) http://ls1tech.com/forums/showthread.php?t=216214
MPG results of my recent fishing trip.
Kearny to Cape May, NJ , 170mls each way.
Road used GSP
Cruise control at 68-69 MPH, A/C on.
200 lbs of Tuna (bluefin) in the bed on the way back
2000 Sierra 5.3l 4x4 ECSB
275/60 R20 michelin LTX M/S (mud/snow tires) (33" overall diam) @ 35 PSI
Uncovered bed with gate closed
87 Nelson Tune w/All TM removed
Amsoil synthetic engine oil and trans fluid
LT1 electric fans
MPG AVG == 17.46