I think your situation is interesting for sure, with the stipend.

GMs 6.6 gas has been very reliable, no DFM, initially I thought it would be a bad idea due to gas mileage, but company is paying for that so it's not an issue. Easy to maintain, actually easy to work on, they really don't tend to have many issues with these. Probably the simplest engine design of the bunch and they have a good track record, been out a while. No DPF/DEF/EGR Diesel/Turbo(s)/Regen is nice. Their transmissions are usually the maintenance item. You could consider NextGen valve body kit in them and it might get you further along than most. Resale would probably be higher on HD 6.6 gas than the half tons with higher mileage. I know a friend that switched their entire fleet from diesel to this 6.6L gas from GM, he said they haven't had any issues with them. They drive all over Colorado, over mountain passes 11,000ft + towing trailers every week. The transmission valve body is really the only issue they've had but it was fixable. I'd say away from the 24s, mid 25 or newer probably better with valve body.

The Ram diesel I find particularly interesting because the company is essentially paying for your truck (assuming stipend is large enough), and fuel/def which is huge with the cost nowadays, but the resale value would be much better on the 2500 diesel than any of the gassers at 200k. Yes, a diesel repair can be dramatically more expensive. Injectors, HPFP, turbo, DPF/SCR, etc., but you're also giving the truck a much easier life than someone who uses a diesel for short trips and towing once a month. It's interesting for sure, maybe more risky though with the high ticket items if anything goes. You could consider an aftermarket powertrain warranty though, for piece of mind.

I do like the Ford 2.7L and the 5.0, but for your use case I'd lean 2.7L, I think it's very reliable when cared for. Ford/GM transmissions I don't like as much as the ZF. I think all 3 can be reliable with proper maintenance but Ford/GM tend to have a lot more issues reported, many around 80-120k+, then some make it 200k without issue, it seems like luck of the draw. The downside of the Ford 2.7L and 5.0L is the wet oil pump belt. Many techs say to replace it at 150k, can't recall the official interval but maybe with highway mileage 200k isn't a stretch for it. Probably around $3,000 to pay Ford to replace it.

Ram hurricane I agree with you, seems awesome so far and great for highway, but it hasn't been out long enough to say the majority hit 200k without big issues. The ZF trans has been out long enough to say it's very solid...so that's a plus.

GM 2.7L has been very reliable, the best of their 3 half ton engines. It's also going to one of the easier engines to work on out of everything listed. Single turbo (accessible in worst case scenario), easy to access everything else with inline 4. There have been many reports of them eating oil more often around 100k...but they've been out for a long time so they feel almost as proven as the Ford 2.7L.

This is a tough call...honestly I normally feel like I can point someone in a direction better than I can here. If it were me and the stipend was big enough, I'd probably look at the 2500 Ram diesel/GM 6.6 gasser first just because you'd benefit from the resale value personally, but if you really don't need a 2500 it might not be worth the risk. Then look at the others as alternatives. I hope this helps...some, but you are right it's a tough call.