The truck has been owned since new by my family (the second, our first was a 92). ... it's got DBA slotted front/rear with EBC greens and motul brake fluid....
Everyone has given you some very good advise for ensuring your brakes are performing "as new" before getting too crazy.
I suspect that the root of your problem lies primarily with either the EBC green pads, a failing master cylinder, or the possibility of needing to perform a more thorough bleed with fresh fluid. I have not EVER heard positive comments on EBC brake pads related to stopping power and fade resistance. Especially the green pads. Especially on a vehicle as heavy as the 80. I only hear them praised for their low amount of break dust. I'd rather stop and make some dust. I believe that a high quality carbon-metallic pad pad should be used on the 80 for best fade resistance.
I personally have ventured outside of the "all Toyota parts" camp, and am trying the following combo:
Fronts - Performance Friction Z-rated carbon-metallic pads with Brembo OEM replacement rotors (good quality rotors and cheaper than CDan)
Rears (Not Yet Installed) - Hawk LTS carbon-metallic pads with Toyota Rotors (no Brembo rear rotor available and I don't know if I trust the cheaper parts store brands to hold up and not warp)
Fluid - Valvoline Synthetic Brake Fluid
Stainless brake lines (future)
As far as your quest for a Big Brake Kit, the chance of keeping the cost reasonable is slim. The only cost effective changes that I see MIGHT be:
1. Larger master cylinder from a different Toyota application to improve brake response. This should shorten the brake pedal stroke required to achieve high braking force at the risk of now making your brakes touchy.
2. Larger diameter rotor and caliper mounting spacer. This would increase your swept area, and mass for heat dissipation. Would definitely advise pads with a compound capable of handling the increased heat, as well as more frequent fluid changes. Also may require larger rims to fit the rotors and calipers. You may have to use a two-piece style rotor and machine your own hats and caliper spacers. Possible, but will require a fair amount of work and investment on your part.
Good luck!