G, you're not going to like this but, I noticed the same difference between my 77 and my 92, both with 12x3 drums. I think it may be a leverage problem at the pedal, the 2 body styles have different pedal assemblies.

That said, the more I used the 77, the better the brakes held, this tells me it's a contact problem, at least part of it.

Couple of notes, new drums MUST BE ON THE HUBS AND TRUED. The factory did it this way to minimize runout of the assembly. Ditto for rotors. I have seen some pretty wobbly hubs and will true them up separately. This is why on car lathes were invented.

Getting to the contact problem, matching the arc was mentioned before and here's a little trick for checking it, find a socket that has an od that matches the od of the anchor pin on the backing plate. Assemble shoes, adjuster and socket into the drum and see if you have full 360 contact.

I did this on the 92 and the brakes are excellent. But it's the long distance tow vehicle so no cheating on it. The 77 is a plow truck junk hauler pos, I just keep clicking the adjustment up .

One other thing, half tons have a bellcrank on the frame that might be able to give more pedal leverage on the drum levers. Iirc, on half tons the cables are connected in a fashion that reduces leverage, should be no big deal to rearrange the cables to do the opposite.