I would say that the first thing is that there is a popular perception/misconception that for towing you need a diesel. A lot of first timers are told this by the unscrupulous salesperson who has a vested interest in selling what's on the lot. Add to this that often times a guys buddies will tell him its not a real truck unless it has a diesel. When we ordered our 2020 30' Airstream I knew that max weight would be just under 9k. From a number of people I talked with (my uncle is a retired truck mechanic) and the research I did online, I easily determined I did not need nor want a diesel. If you are in the 10 to 12k or less range a gasser is a great alternative. You lose almost 1000 pounds in payload by going with the diesel. Therefore I don't see how it makes sense to get a diesel in a 2500, especially the MegaCab. And as I have said before, please don't get me wrong, the Cummins diesel is an awesome engine. If you tow heavy and often it is the way to go. But most guys out there don't need it for what they are doing with the truck. Now if money is no problem and you just love the sound and torque of a diesel, then fine, thats what choice is all about. I would rather not deal with the diesel emission fluid and regen issues. My truck is not a daily driver and will sit for weeks at a time. But when I tow it performs flawlessly. Plenty of power going over the mountains.
It's unfortunate that dealers don't seem to stock the big Hemi in the higher trim levels. I would just say to everyone, for as much as you are paying, why would you not want to get exactly what you want. To me ordering almost always make the most sense. You can still negotiate price and will get whatever incentives are in place at time of delivery. Yes I know it sucks waiting (ours took 3 months) but it's worth it in the end. We did the same thing when we bought my wife's 2019 Pacifica. We ordered it so we could get the spare tire instead of the stupid vacuum, plus we wanted the tow package. Best of luck to all and safe towing!