1/2 ton brakes not what they should be?

[bfr57]

I've had my 71 1/2 ton 4x4 for almost 20 years and have never been real happy about the brakes. I have factory disc in front and drums in the rear running a 31x10.50 tire. I've tried many different things from new masters, a dual booster from a 3/4 ton, bleeding the snot out of it, stainless brake lines. The pads/shoes are just over-the-counter items. The rotors/drums are all within specs also. Even in a panic type stop, the rears won't lock up! Is there something I'm missing? Would high performance pads/shoe help? Could proportioning valve be bad? If I put 3/4 ton axles under it, would that help? Not sure on a 3/4 ton Dana 44 if they run same calipers or not, but I'm sure a Dana 60 is bigger. Now don't get me wrong, it isn't un-safe to drive, but feel they should be a little better. Any ideas would be appreciated!