1998 Dodge Ram brakes

I have owned dodge 4wd trucks of various years, '87, '92,'98. All of which had rear drum brakes. Anyone that has had one of these knows that the rear brakes do basically nothing , on slick or in wet grass the , the front discs will lock up and throw you into a slide while the rear just keeps doing very little.
I have adjusted them and even replace all components, and still they only work decent for a few days.
Plus they never seem to self adjust, and yes all the cables and adjusters are new.
Is there a problem with the proportioning valve or lines ,that keep these from working, and does anyone know of a fix . Thanks, John