True MPG's for a Diesel P/U??

Talked with a siding contractor that runs a '17 1 ton crew cab 4x4 with a Duramax diesel. Somewhat teased him about his 18-20 mpg that I've heard/read about and he flat out laughed  . Said that "can" happen unloaded, going downhill in neutral WITH a tail wind  . He said once he hooks up the 24' tandem axle job site trailer, mpg goes to 7-8  . Where's the cost benefit between a gasser and a diesel? I thought I had it bad with my 5.4 at 9-10 mpg LOL !! 

I will say that the enclosed cargo trailer's contents(supplies/tools) weighed closer to a "loaded" 220

what IBWD Mike says. there are very few that will ever actually realize the economy of a diesel. they cost more to buy, cost more to operate, and their slightly better mileage will not cover the difference in gas/fuel cost. True, diesel has a bit better performance, but, for most of us the small difference in performance is not worth the cost.

that make ad on boxes to get you better mileage and power when needed. my '97 1 ton 4x4 has one on it when I bought it. it allowed me to get on average 27 MPG with my 6,5 Diesel. my little box don't have a sticker on it so I don't know what brand it is. it also allows me 13 different settings depending on what is needed. I've never pulled a big loaded trailer with it, but just drove it for the excellent ride and mileage. I can change the settings of the chips and the turbo boost by turning 2 dials on the dash.

The real problem nowadays is the lower quality fuels. The cetane rating for diesel used to be 50 or above 25-30 years ago, now all you can find is a minimum of 40. Occasionally someplaces will be selling “premium diesel” at 45 minimum cetane. My dad go one of the first 5.9-5speed Dodges in 1989, it has a 3:54 ratio rear and is 2wd. When is was new and fuel was 50+ cetane it would get 30+ when running empty and keeping the RPMs down, loaded it would still get low 20s pulling a trailer. Now even with adding cetane booster/injector cleaner to the fuel the best it can do is about 22 MPG.
   I got a 93 new with a 5 speed and 4:10 rear 2wd and it could get 17-18 MPG on long trips pulling the trailer at near to 20,000. To do that I had to stay in the right lane and under 62 MPH. If I kept up with the prevaling traffic, MPG would drop. Now thw the cetane is lower, its a stretch to get 14-15 loaded and driving easy.
Today everone “must have” a 4wd and they have no idea how much extra fuel that wastes. Along with the latest pollution particulate filters that need raw fuel sprayed through them to burn them clean. All the added truck weight of the 4 door cabs and the multitude of electronics has to be moved, the engine doesn’t know if it’s pulling against payload or truck weight, it’s all the same at the back of the crankshaft. 70 mile and hour and above speed limits are doing nothing for fuel economy. Most people are doing 80 and above around here.

Paul B is right on it , the quality of fuel is a big factor,, this junk chit MFA/ Breaktime sells wont even start a brush pile on fire

My 1994 Chevy Silverado 1500 5.7 gas, 4 speed auto, 2wd gets 16 unloaded and 8-9 loaded pulling the Wd45.

IBWD MIke wrote: I have a 2003 Dodge with the 5.9 Cummins in it. It was my dad's truck, I ended up with it after he passed. It will get around 16 mpg empty, maybe 13 to 14 pulling a WD45 around. Here's the wildcard, the onboard computer tells me I'm getting lots better mpg than the math when I fill up. Usually about 15% or so. Driving around NE Wi. a couple years back the average economy showed over 20, not sure how far it was off that time but I'm sure it was not right.