My Tundra with a 5.7L V8. Cannot average more than 13 mpg, and I saw 18 mpg for a split second while going downhill. Just a bulletproof of an engine/truck though, I cannot believe how much I like it. The truck is getting about 70% of work load vs my M's, if not more.
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Current:
16 F82 M4 GTS, Black Sapphire/Black, DCT
08 E92 M3, Sparkling Graphite/Bamboo Beige, 6MT
07 E85 Z4M Roadster, Alpine White/Red, 6MT
99 E36 M3, Techno Violet/Dove Grey, 6MT