As a rough guide my thought are:
12,000 lbs gross weight is my limit for a 3/4 ton. Single E rated tires have a total weight limit of just over 6,000 lbs for the rear axle.
My dually with 4.10 gears has a limit of 13,500 lbs for towing due to having a gas engine. This is a tow limit. Even with 3,000 lbs of pin weight I still have 2,500 lbs of load capacity.
Anything over 14,000 lbs gross should have a diesel powered dually.
I hear the screaming. Every truck has different options that affect the numbers. A standard cab will have larger numbers than a crew cab because it comes with less curb weight from the factory. Just to many variables. So when you ask a loaded question for finding the right rig without posting numbers and facts you really can't get the answer your looking for.