We have a 1995 E-350 with a 7.3 PSD. I would like to know if there is any performance upgrades I can do to make it more efficient while towing. The combined weight of the truck & trailer is about 15,000 lbs. I think the rear axle has 3.55 gears. I know there are not many upgrades available. I thought there might be a different turbo or something. I get 17-19 mpg unloaded and 9-10 mpg at 15,000. Will any parts for the F-series fit.