2001 Tahoe with a 4.8L, s&b CAI, Hypertech Max energy, and a series 40 flowmaster. Just got 18.5 mpg on my last tank. 100% in town driving.
I haven't tried any type of synthetic fluids, but those are next to be phased in as maintenance demands. I am thinking Mobil 1 synthetic motor oil w/k&n...