I'm pro 6.0L personally....maybe I'm just biased because I own one
Depending on how you go about it, if you added it up, I bet the annual costs to maintain/fuel a 6.0L gasser and a D-max aren't too far apart. I have a 2002 Saturn L200 with a 2.2 Ecotec 4 banger in it that averages 30mpg's and my truck roughly averages 10-11ish the way I drive it....I drive them both almost equal amounts of the time, so overall between the two vehicles, I average 20mpgs. Look at it that way and it's not bad at all.
*With a Diesel, you have higher cost of fuel, frequent fuel filter changes, more costly oil changes, **** that can go wrong with them that ain't cheap to fix like turbo parts, glowplugs, injectors, etc.
*With a gasser, you have shitty fuel economy, but it's majorly low maintenance.....cheaper oil changes, cheaper fuel, and the 6.0's are pretty damn good motors and my 4l80e tranny seems to do the job well also
I'm content with my truck and don't intend on selling it anytime soon. Will list specs below, but I drove it to Auburn (3 hr drive) without towing anything and nothing in the bed and it got 13 1/2 mpg's and that's calculating miles:gallons of fuel...not reading it off the message center in the dash. And I also have 33-12.50 tires on it so the miles I racked up on that trip were actually a bit on the short side from the speedometer and odometer being off from the bigger tires. So maybe even 14 actual mpg's.
2006 GMC 2500HD, 6.0L gasser with 107k miles, 4L80E tranny, crew cab, 4:10 gears, Single Flowmaster, 4x4, 33/12.50/20 mudders (32.8" spec diameter) on 20x9 rims.....best recorded mpg's = 13.5. Street driving around town = 10-11mpg's. Towing hard up and down hills on interstate at 80mph = 7-8ish. Just regular towing at normal speeds 55-65mph = I've gotten up to 10mpg towing.
For what I tow, it does the job well.....now some of you pulling a 30' gooseneck with two rigs or whatever on it....I'm sure it would be worth it to stay diesel, don't think my truck would fair well under those conditions.