Long Downhill Brake Fade!

[swissarmychainsaw]

1973 Suburban 1500
350/350

Had the truck for about a year, took the family on some deserted back road and encountered a very steep and long down hill. This, on the brakes for 15 mins, going really slow, steep, winding one lane road.

At some point my brakes overheated, and I got massive pedal fade.
I stopped and the rotors/calipers were smoking a bit.

I think to myself, "I'm going to fix this! Having your brakes disappear sucks!"

(several months later)

Replaced:
* New pads
* Front Brake hoses (rubber)
* Master Cylinder
* Brake Booster (did not seem to be keeping pressure)
* Front Rotors
* New fluid
(also did wheel bearings in front, and tie rods, etc.)

I did not touch rear brakes, which show about 1/3 left on the pads.

THEN, I took the Burb out camping again, and came down a steep slow downhill, and YEP. It happened again. Brakes get hot, fade, and I lose pedal.
(It felt like I lost power assist. It would stop but I had to really put some force on it.)

What am I doing wrong here? I really want this thing to have brakes that I can trust you know?

Thanks!