Flex fuel won't matter. There are really only two tuners available for the Titan - the Bully Dog GT and the Superchips Cortex. Not sure if the Superchips is still in production, but these two work. Depending on your budget, however, you might consider getting him an upRev tune from Seymore here on the forum. Easiest way to contact him is likely to call or email the folks at Cajun B Pipes (cajunbpipes.com) as he does their tuning. From a performance standpoint, upRev is the hands-down best out there, but it's a bit more expensive than a Bully Dog.