I know I'm responding to an older post, but this is the eternal question so I will play. This is the argument like others that play out among gearheads every day. Ford vs. Chevy. Dirt vs. Asphalt, etc.
A little background.....I'm a diesel mechanic by trade and despite what academia or "environmentalists" may think about that, I love what I do. At work, I work on everything from semi tractors to heavy earth moving equipment. GOD has blessed me with a lucrative means to make a living and support my family. I'm a kid that still plays with trucks, but just on a larger scale. Enough about that.
The irony is the fact that BOTH of my race car haulers are gasoline powered. I use my crew cab to haul to local tracks and the motorhome for longer ventures. I'm in California, but I know most of you are from Texas. GOD willing, I would love to make it out there to race, hopefully before the end of this season. I picked up the crew cab from the truck dealer I worked at the time. It was a trade in that needed some transfer case work, so instead of doing a recon, they decided they were gonna wholesale it, so I picked it up. When I was looking for a motorhome, a diesel wasn't really an option in my price range. I picked it up used with only 18K miles. The guy I bought it from couldn't get it to pass smog, so I took it off his hands. Both of them are powered by the latest big block, the GM 8.1L. I would love to have a diesel, but both of these machines kinda came across at the right price at the right time. That being said, I have no regrets and I will tell you why, besides the fact that they are both paid for. No loan payments!
I would say that if you can afford it, go ahead and spring for the diesel. If you can afford a DMAX, the 06-07 VIN D LBZ is the best pre-emission engine made. It starts @ 650ftlbs of torque, but easily responds well to minor tweaking. If a pre-2000 truck is more in your price range, spring for the 1998-2000 Classic with the 6.5 VIN F engine. The later ones have dual thermostats which takes care of some of the earlier overheating issues. ANY truck you buy whether gas or diesel should have the hoses replaced along with a new cap. Use the best parts you can get; Continental, Gates etc. Try to get their fleet grade stuff if you can. As said in an earlier post, use an injector driver relocation kit to keep it cool. Use a cetane booster/ fuel conditioner from either Stanadyne or Motorcraft to keep that injection pump alive when running ULSD.
In my opinion, gas engines have come a long way. Although unheard of 20 years ago. It is not uncommon to see the LS engine go 200-300K without using a lick of oil. At the truck dealer I worked at, we had an account with Bragg Crane. They had a huge fleet of trucks using the LS engine. Many had well over 200K. These trucks were not babied by their drivers by any means. If you kept clean oil in them, they would run forever. Engine oil technology with synthetic becoming more affordable and mainstream has extended gasoline engine life significantly. I work with a fleet where many of our Ford F250s have the 6.2L engine in them; many over 200K miles, no valvetrain noise. We have a few V10s with over 300K on them. Our linemen cover from Southern California to Nevada and Utah. They would take these trucks without thinking twice.
In conclusion, it is a personal and financial decision you have to make. The DMAX is little more expensive to purchase and maintain, but overall a good engine. The 6.0 is reliable but may spin hard pulling a grade. It may take some mods(intake, exhaust, camshaft, programming) to make it better. The 8.1L is good, but severely detuned from the factory. Oftentimes, just taking off the torque management makes a big difference.You can do mods (intake, exhaust, camshaft, programming) to approach diesel torque numbers but fuel mileage will still be better in those early DMAX engines. Later DMAX engines with aftertreatment (DPF & DEF) experience less MPG and less longevity.