I think it depends on where you will be driving for how much overweight you can be "safely". Eg, braking going down a long steep mountain road at highway speed is different from in town on a flat road. I don't know how they "rate" brakes.
Bad braking is a thing of past years with the later gen model LDT size trucks.
Brake on a LDT are the function of the axle ratings ...at a minimum.
A 3500 drw GM may have a 9375 rawr and a 6000 fawr for 15375 lbs of braking performance. I haven't seen the OP cert placard gawrs and may look like these numbers.
At some point GM uprated the 3500 drw rawr to 10500 lbs = which would give this model drw a 16500 lbs of braking performance.....at a minimum.
Hooked up with a 24000 gvwr GN flatdeck or a stock trailer with three 8000 lb axles = 40500 lb of combined braking performance. This is how commercial haulers/ car haulers/cattle haulers can legally/safely operate at these gross combined weights and still carry up to max axle loads.