@sheath, damn, that 7.3 powerband is impressive. That was going to be what I ordered if the local chevy dealer didn't have the L8T coming in so quickly.
@nards444I have a 2022 L8T, and I only have a couple gripes about it. But towing isn't one of them. It FEELS sluggish, but it's really not that bad. If you try to gas it while it's towing, it scoffs at you, and basically says, "I'll get there, gimme a minute, geez....". Going from a 1500 to a 2500, it just feels like I'm going slower than I am. When I'm cruising at 65 towing, it felt like I was going 40. Not a bad thing. The exhaust is pretty quiet on the L8T too, so I think thats part of the perception. My 5.3L seemed throatier and was noisier in the cab.
I'd say if you're only towing ~10x / year and worried about tow mileage , I think the fuel cost difference would be fairly negligible, especially relative to the extra $10k for the diesel. Definitely factor in that added cost when doing the fuel cost savings. If you only plan on having the truck for a few years and trading in, it may not be worth it to go duramax. If you plan on keeping for the long run, might pay itself off.
That said, I just towed combined weight of 16520, with 7240 on my trailer axle for 3 hours. I got about 8mpg, but it tows so nicely, especially compared to my 2019 5.3 1500 i just traded in. I don't have hill descent help, but i never really had to tap the brakes coming down grade, which was about 6-10%. It just held at 55mph and didnt struggle or anything.
I was able to get from 55-70 pretty easily to pass semis when needed, but I think those are the instance when I wouldve really felt the difference with the diesel.
Ultimately for me, I decided on the L8T over the duramax because 1) availability, 8 days from deposit to delivery and 2) my normal commute (getting about 11mpg) is pretty stop and go. I felt that would be bad on the diesel being in regen like 98% of the drive time, especially for an extra $10k. IU only tow my travel trailer about 10x year, so didn't seem worth it to me.
If you currently have a diesel, you might miss it. The other factor might be based on your driving routes. My full 36gal tank is only getting me about 400 miles tops probably on the highway, though I haven't done much of that driving. If you're running a long ways through barren land, it might be worth it to have the extra mileage of the diesel. But I really like the L8T.