I installed a hypermax Econ tuner several years ago and it improved my mileage by 2-3 mpg both towing and solo. Two years ago I towed my 14,000 lb fifth wheel from Florida to Yellowstone and averaged 12.5 mpg. One 400 mile stretch I averaged 14 mpg. I went back to the stock tune when a Ford dealer said that my tuner was causing coolant to blow out the degas, but that didn't help the problem so I reinstalled the ECON.
Without the trailer I get 19 mpg in town and average about 22 mpg on the highway. I drive like an old lady, though. I usually don't go over 65 and use the cruise control.
2006 F-250 Superduty with 6.0 diesel
Unfortunately, that's the conclusion the repair shop came to on Wednesday. I decided to got the whole top end upgrade and they're going to do it for $6800. It includes a valve job, new ARP studs, upgraded OEM oil cooler, EGR cooler bypass, a different programmer to eliminate the check engine light after the cooler is removed, new fuel rail O-rings, coolant flush, coolant filter, etc. He had a full legal-page of upgrades. He's also going to check the injectors.Your head gaskets maybe shot if you are blowing coolant out the degas bottle. You can get a test, at a local auto parts store, To test for the presence of CO2. If it is present your head gaskets are shot.