Flex fuel means that it can run on E85 and it will run on today's fuel of E10, however if you do manage to find some actual regular unleaded gasoline without the E rating it will run on that too in fact it might even run a little better, but none of the stations will put that fuel in your vehicle, only in a gas can or an older carbureted vehicle or tractor.
So if your rig does not have FlexFuel any where on it stick with pump gas and use top tier fuels, and maybe every other tank of fuel add a bottle of Techron to the fuel tank, this stuff really helps keeping the fuel system clean, I have been using it for years and none of my rigs past or present have had any injector problems, in fact it even cured one that I had bought that just started to have a partially plugged injector. HTH
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