Right now I have 2 with gas engines, a 2000 Chevrolet cew cab dually 4x4 with 3.73 gear, 454 engine, automatic overdrive transmission with 90-k miles.  Unloaded it will get around 12 on the hwy with the cruise on and loaded it will get around 7.  The other is a 2002 Ford F-350 regular cab dually with a flatbed, V/10, automatic and gears I have no clue.  Unloaded last weekend I was getting close to 15 with the cruise set driving on the hwy.  Have not tried it loaded yet.

2001 Chevrolet 3500, ext. cab, dually, 4x4, 8.1 gas, Allison 5 speed, 4.10 rear axle, stock all the way, closing in on 90000 miles. Pulled 10000# trailer last weekend from Rocky Mount NC to Hickory NC, got 9.12 on the trip up and 12.87 running 75 mph on the way back home empty. It will get around 8 mpg running 65-70 pulling 15000#. All time low was 7.2 mpg loaded running 75 mph into a 25 mph head wind.......

If your looking at a Ford, they say the V10 with a 4.30 rear axle is pretty hossy, stay away from a 5.4 V8 in a dually, it has a hard time just moving itself around, let alone pulling a trailer.

I have the same truck as Retento ... 2001 8.1 gas engine with Allison transmission.   The decision point was cost.  The diesel option was $4500 more.  I just don't put the miles on to justify the first cost and added maintenance.  Years ago, gas engines were higher maintenance.  With 100,000 mile tune-ups (platinum sparkplugs, no distributer, fuel injection, single battery,  synthetic oil, long life coolant, etc) ... today   ... Diesel is more expensive to maintain and fuel cost (Ultra Low Sulpher) is closer than before...

Of course, some folks just like diesel noise and stink to announce their entrance. 

I have the same truck as Retento ... 2001 8.1 gas engine with Allison transmission.   The decision point was cost.  The diesel option was $4500 more.  I just don't put the miles on to justify the first cost and added maintenance.  Years ago, gas engines were higher maintenance.  With 100,000 mile tune-ups (platinum sparkplugs, no distributer, fuel injection, single battery,  synthetic oil, long life coolant, etc) ... today   ... Diesel is more expensive to maintain and fuel cost (Ultra Low Sulpher) is closer than before...

Of course, some folks just like diesel noise and stink to announce their entrance. 

First off these are NOT my personal trucks, I am in the used car buisness and buy mainly 3/4 ton and larger trucks to sell.  The Ford done fine loaded and unloaded, would much rather use a diesel any day.

My personal truck is a 2007.5 Dodge 3500 c/c with the 6.7 Cummins and 6 speed automatic.

When I buy a truck and offering it to people that tow or haul heavy loads, I want to check the trucks out myself before I tell someone that the truck will do the job they are needing to do.  Nothing I hate worse that not having enough truck to do the job I need to do.  That is why if I can use it myself and haul either my horse trailer, my loaded hay trailer, dump trailer or even my 3 car trailer with I will be able to let my customers know what the truck can and can not do.