My experience, which is nowhere close to some other here, is that the gas trucks tend to nickel and dime you over the course of ownership while the diesel trucks tend to go a long time with nothing but when they need it it cost a lot.
Some complain about the oil changes costing a more but the intervals are further apart too
From what I have seen, and delt with myself. Gas trucks have coil packs that go out it seems on every make and model. Plugs, wires. Several with evap issues. Oxygen sensor problems. Throttle valves, distributors, fuel pumps, etc.
Most of these don't cost more then a few hundred. Most far less. But it seems they happen more often but because of the lower cost people are less shocked and pay out without hesitation.
For the Duramax, 11-16 has the rare but possible fuel pump issue that can take out injectors with it. probably no more then a few percent of the trucks will have this but can set you back thousands. The LB7 had injectors that when bad prematurely. Again could be several thousand dollars. When the emissions where tighten up and EGRs, DPFs and urea injection was implemented, it had growing pains. Most of that has matured to the point where it isn't much of a concern anymore. Just remember, when emission controls first went on gas rigs people hated them and routinely gutted cats or removed them. Now most don't even think twice about it. Diesel is not far behind
When it comes to the rest of the truck. Most everything else is the same. Steering, wheel bearings, suspension, electronics, etc
I say to each their own. I have no need for a diesel, don't pull enough to justify it. But I wouldn't have anything else