x2.
The GMT 400 hydroboost braking system is well designed, and underworked, especially in the duallys. my boss had a 98 C3500 BBC 4L80E and he routinely towed a tandem dually gooseneck loaded with tractors, definitely over 20K combo. he owned that truck for a year or two and never bought a brake controller, he said the brakes on this are way better than his dodge/cummins' so he never saw the need to run trailer brakes on that truck.
my PS pump is going out on my 99, and we are still running it, and the brakes are adequate.
we did feel like we needed more brakes one time on the 92 HD, but we were closing in or possibly over 30K with no brakes other than the truck.
I would say run it!