Well I have owned what you have and now own what you want. What you tow as in weight and what you want to tow, and how often and how far all matter, along with what you want to get out of it. If your towing a the limit and doing it far and long, moving to the 2500-3500 platform will be you best bet. 3500 really isn’t necessary, but if you want the added capability for a extra bucks, so be it.
For reference I have owned a 2011 and 2015 3.5 ecoboost, 2021 Chevy 2500 Diesel, and now a 2022 GMC AT4 gasser
With that said I have owned two ecoboosts and as a whole have been the most capable trucks I have ever owned for what they are. So if your talking a HD gasser, the ecoboost actually has 50 more hp and torque then the GM 6.6 gasser and the ecoboost will have a flat line torque curve, meaning you get it all the same time vs over 3-4k rpms. Motor wise the ecoboost acceleration wise will probably haul the same if not better then the 6.6 gasser and also get substantially better mpg when not towing and probably the same when towing. My ecoboost typically got about 17-18 all around mpg and 12-13 towing 10k lbs going 65, where as my gasser in my GMC does about 12-13 all around and slightly less towing. The difference is the bigger truck will be able to haul more payload and towing weight, and will also handle and stop better then the smaller half ton truck.
No comparison with the diesel and the gasser after owning both. You want the worry free towing, accelerate when towing, and get descent MPG get the diesel. The gasser IMO doesn’t hold a candle. Your going to pay more for the diesel, 10k more, and fuel right now is almost 2 bucks more a gallon, you save about 20% on that due to mpg increase. But the bottom line between maint and fuel you will never save money on the diesel, but you will also get a better return at trade in time. But if you plan on owning 15 years that might be moot point, but might be another reason to go diesel. In a way I regret getting rid of the diesel, but reality was I hauled a boat 10 times a year 15 miles amongst some other smaller thing, and in the whole equation going down to the gasser saved me money.
Lastly look at trim level levels and exactly what you want and need. I wouldn’t necessarily zoom to the Denali or HC after comparing apples to apples. My AT4 was option to option compared to the denali. I ended up saving 5-6k, and the only difference was badging, grill, and wheels. Same can be said for Chevy. High trim options merely add all the options and change out the wheels and sometimes grills and charge you more. I say typically because at times you can pay more for a lower trim level if you do not know what you are looking. Buddy of mine was bent on a Denali and told him the same thing. He ended up with a Carhartt edition with everything he wanted for over 10k less.