My 02 with a 5.3 had Flex Fuel. I tried it once. Mileage sucked and so did power which was an issue when towing a trailer. Ran that tank as dry as I dared and filled it up with the good stuff. Never again.

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01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow