Working on improving fuel mileage, 2010, f250, 6.4, fx4, superduty, supercab. purchased at 45,000 mi. started out at 12.4 mi per gal, new fuel filters were installed at dealer at that point. complained about mpg, they did a recall item re fuel, at this point mpg improved to 14.4, city & hwy. I'm using the ford cetane booster as they reccomrned. 65-70 hwy speed. I have yet to tow my 30 ft rv. I found a gov. site that gives good easy to understand info on diesel fuel. "eia" u.s. energy informaton admistration. I've tried arco/bp, texaco, stories cle elumn wa, chevron w/ max. b5. due to more hwy mi last tank average mpg 15.7. 9-23-2011 installed michelin ltx ms2 275/70/18. I'm hoping this will improve mpg. So as not to void my bumper to bumper warranty, I'll be talking to my dealer about chips and air filters, trying again to improve mpg. Looking for ideas.