ABS "triggering" when it shouldn't

[Myke456@aol.com]

During the past 12 years I've spent in my 87 5kcsTQ, I've fixed a few minor 
ABS related problems. In all these circumstances the ABS OFF light 
illuminating (and shutting off the system) always clued me, that a problem 
existed.

Current problem:
While driving, when I apply the brakes the pedal will feel stiff and high 
(hold on-don't jump to the bomb answer just yet), while I can hear/feel the 
ABS system triggering against my foot, and the car barely slows down. 
Increased pressure will sometimes "release" the ABS and normal braking 
occurs. The ABS OFF light does not illuminate. In essence, the ABS system 
seems to be keeping braking from occurring when it shouldn't be. Braking 
works normally when the ABS is switched off manually. 

Consider the following:
above driving any speed, dry paved road
bomb is a few years old, but takes 30+ pumps before stiffening the pedal
master cyl less than 6 mo. old
sensor caps recent and positioning OK

I don't recall a problem like this posted to the list in the past. Any ideas?

  ([____]=====OOOO=====[____])   87 5kcsTQ, 242k miles
     Mike Aiello     original owner      Dutchess County, NY