I've looked into it a bit with my Mav, It's a 4.2 auto and loves to consume fuel. From the info I found the deisels aren't that much better. I got good results from a few thing the best was when installing the snorkel I did away with the factory intake ducting and factory cleaner as they flow like S&*T, and the exhaust heats the duct which inturn heats the air passing through it, I ran new ducting over the front of the rocker cover and it stay's very cool and got a massive improvement especially on the hiway.