My sierra did the same thing after some 'hecktic' hills driving BUT I kept on driving and the next day the caliper locked on and seriously frucked itself. (nearly pulling the car and myself off the road and down a nasty as hill :S)
Either buy a rebuild kit (if you can get the one with new pistons go for that) or take it to a brake specialist and get them to rebuild the calipers. If they change the pistons make sure you get old ones back so you know they have done it right

Dave

Alien's description does not sound like what happened when I boiled the brakes in my commodore. I just progressively lost braking ability.

Progressive loss of braking ability - aka brake fade - is more likely to be a friction surface (pad/rotor) issue, than a fluid boil issue - when the fluid boils, like Gwagensteve says, you'll have no brakes.

It takes a while to get the fluid up to boiling point (which will vary with the moisture content), but once you get it to that point, you're going to go from full-brakes to no-brakes in the blink of an eye - total brake failure, akin to fluid loss, with one exception, give it a chance to cool and they work again - that is, assuming that when they failed you didn't stuff the vehicle, so you get the chance to find they work after cooling off.

Perhaps an opportunity toupgrade to lwb vit discs and calipers ?

That's a no go - the caliper won't clear my hi-steer arms =) been there, done that.