try ceramic brake pads....they actually bite better after they get warm but will last longer and resist fade.
but seriously, you need to make sure you entire brake system is fresh and that you have properly functioning trailer brakes. also consider your driving habits in areas where conditions put a big load on the brakes. don't crest a hill at top speed....slow down and shift down to help hold back rig and trailer on the downhill.
air bags are good but expensive and add complexity. i prefer just upgrading the rear spring packs with an add a leaf kit or more leaves. a 3/4 ton suburban or pickup of the same vintage should be able to donate some spring packs that fit (pay attention to 2wd vs 4wd). 1/2 ton rear springs are junk on a vehicle hauling loads. i have a 72 burb 3/4 ton 2wd with stock coil rear suspension and i plan to swap out the coils for the HD option units.
