The only option on the 2015 and newer 6.0 HD's is with 4:10's.
I have owned both 2015 6.0 and Duramax and pulled 30K plus combined with both. I never seem to get the diesel mpg advantage others get. Pulling that weight at 5-8K feet. I would get about 5-6 mpg. I get 8-9 with an '18 Dmax and about the same with my '15 duramax.
Obviously the Dmax pulls better with much less effort. However, I didnt mind the 6.0. I put my foot in it and let it whine. That really is an incredible motor. The biggest surprise is when I traded out of it. I got great resale out of it. It cost me .18 cents a mile to own it.
I think for such a light load either would work. If you were pulling more weight it would be clear but at 10K you have more of an option. If you have the money to put into it, I would get the diesel. Standard or long box. I get the long box but I have to work out of them. The longer wheel base can help with stability, but at this light weight I dont think it matters.
