towing with gm 6.6 gas

Mine is a bone stock LLY. Transmission has never been apart. Engine has never been apart. Original turbo, injectors, etc. When I had the TC I was 1,600 pounds over GVWR and pulling a boat. When I'm working I've had it up to almost 26,000 Gross combination and it's only rated for 23,000. I have no complaints.
Spending an additional $10,000 on the diesel and then having to buy fuel filters and DEF is a tough decision.

^Is your lb7 or lily bone stock? If so, the gasser won’t be a huge disappointment. Only a small one.
If you’re tuned, the gasser will feel like a turd, comparatively…when towing heavy.

I hope to see some good responses here. I asked the same question on the GM truck forum Diesel Place months ago and got very little response.
My own 2005 Chevy Duramax dually is nearing 300,000 miles and I know I need to replace it. I'm on the fence about getting a diesel again. The new 3500 gas has higher axle ratings, higher GVWR, higher GCWR, more HP, and an extra gear in the transmission than my current truck. The only thing is I'd have less torque. I really wonder if the extra HP and extra gear would make up for the difference.

The 6.6 gas has 464 lb.-ft. of torque. The diesel has 910 lb.-ft. of torque. It's your choice.