Last summer I had a 2017 3500HD that I used to tow my trailer until August. Unfortunately, all my trips were 50 miles or less. For Labor Day I take a 300 mile trip, and I was back to using my Express 3500 with the 6.0 gas.
Yes, I did notice the difference. The diesel tow experience was great. Maintenance over the 20k miles was not much more extreme, several DEF fills. Fuel costs were more, but also average over 18 mpg for total ownership.
If I was buying another tow vehicle, I would stay gas for my trailer and use. I have not towed any mountains, and do not plan any trips in the next few years.