Check your vin#, the eighth posistion is the engine identifier. If it's a V then you have the flex fuel 5.4. The regular 5.4's have a 5 in the eighth spot.

Looking for a sticker on the fuel door or the yellow gas cap is not consistant from year to year or assembly plant to assembly plant. My truck is a FFV that was built in dec 06 in dearborn, it has a sticker on the fuel door but has the standard black gas cap. The only way to be 100% sure is check your vin#