If you are comfortable exceeding GVWR (I would be) then with my new knowledge of the axles in the Mega Cab you aren't over max capacity...but you are getting close.
Do you plan to not have much payload in the truck?
With 3000lb pin weight and an avg of 150lbs for 5th wheel hitch...you are getting close to axle capacity...which would start to concern me.
I do agree with the fact a 2500 does have extra capacity...but when you start doing the same with a 3500, you realize something has to give to make the numbers more specific.
Look at GVWR before 2013.
8800 up until then. The 5.7 Hemi still maxed out at 9000. Then the Cummins got 10k and then the 6.4l the same 10k.
I just keep thinking something that isn't rated is what keeps the 2500 "limited"
I have been chasing these payload and tow capacity issues for awhile now.
I am comfortable exceeding 10k...but not 11k on my truck. Capacity is 11500.
With the mega having 12500.. I would pass the 10k...but start thinking hard at about 11750
This would also depend on geography, amount of highway miles at speed, and how often.