A gas long block is $8000 at the dealer, installed. A junky reman'd long block, installed by an independent shop is $6000. I've done both. Fuel system repairs on the diesel are just too expensive and can eclipse serious gas repairs easy. Also keep in mind that the gas engine will require a timing chain and tensioners at some point. Many fleets skip that, and will do a long block at that point. Especially if they get over 250,000 miles on one before it blows up.
$12k gets you an engine and transmission with gas trucks.
Don't forget the uber expensive DPF that might not be delete-able anymore. And plenty of DEF injector replacements. Not to mention 1-2 gallons of DEF per tank of diesel.
Then on top of all of that, my diesel is only powerful when it wants to be. Cruising down the hwy with a trailer. On city streets, if you hit the torque limiter in low gears, the gas truck will sail right by. And the diesel lifts throttle to shift slowly. Around town, and on slow country backroads, the gas engine is more spirited, faster, and more fun.
Hauling a 30 foot TT, yeah I'd rather have a diesel, but a gas engine does that job fine. Overlanding with almost no cargo weight? Gas for sure. Giant tires and a slide in camper?......can go either way depending on exact setup.
It's a race to see who can make a clean diesel that isn't crap. First to do that is going to rule the diesel industry. You get to be the beta testers in the meantime. I'll bet that emissions are overall better at Tier4 levels. Considering regen, and higher overall consumption.
Drop down to Tier3 or 4 rules, I'll be the first in line to buy a diesel engine.