I haven't spent the time to read all the threads, but I put Royal Purple in My rig 3000miles later i am getting 19mpg, highway and 16mpg pulling a 42 Fountain

also Lucas injecter treatment evrey 7K miles

i thought it was good, really didn't know.....i am going back to read about boats now...

Don't figure your milage by the computer they are NEVER accurate. You have to do it the old fashioned way, MATH. I get about 14-15 empty average over a tank. That is driving with average accelerations and 75 on the highway.

What gear rstio and is it a 4x4 ?? That milelage seems way to good to be true while towing. The best Ive seen is 18.5 mpg not towing

i will check on the ratio, i checked the math, it came out to 18.43 its not a 4x4, its also a 5 speed manual transmission, and i use crusie control 80% of the time

14.5 TO 15 in town(6.0 powerstroke with an airaid air intake, basanni 4 inch exhaust and an edge power programmer) 4x4 with auto and 3:73 gears and stock tires. 19.6 on the last road trip at about 75 to 80 mph.
and 13 and change towing a 292 Formula.

My new Duramax only gets 13.5 on the hwy. Thats according to the computer.

2004 6.0 Powerstoke, 4x4, 3:73, auto. 13.5 to 14.5 mostly in town. Haven't pulled boat with it yet.

Forgot to mention truck is crew cab with long bed

2002 F-350 CC DRW Long Bed 4 x 4, 7.3 PSD w/ 4.10 Gears

Bought truck new, has 44,000 miles on it and is completely stock.
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Best Ever Mileage = 250 mile trip under 2000 RPM all the way non-towing. Got 15 MPG

Average non-towing around town and above 2000 RPM
(70 MPH +) is around 11.5 to 12 MPG

Towing 12,000 lbs at 70+ MPH usually see 9.5 MPG to 10.5 MPG

2003 super duty ,Towed 28 daytona tall deck weighed at truck stop without fuel 9600 lbs. Towed from missouri to arizona the best we ever got was 9mpg the worst was 7 mpg. I dont know how you guys do it! It does have bigger tires on it but geesh it sucked fuel.