My 95 3500 has only had 1 set of new rear shoes in 225K miles. numerous sets of fronts. I went to the larger Chevy wheel cylinders last year. They helped. But the factory proportioning is set way safe. With larger loads it could use way more rear bias. Mine carries a 1500lb camper, 6500 triaxle trailer and 3100lb car, plus tools, scooter, generator, etc. Probably north of 19,000lbs. My next swap is to run a bypass in the rear line direct from the master cylinder.