May not be ABS related but a vacuum issue. Your vacuum booster may be trying to tell you something. Put a vacuum gage on that you can read while driving and hit the brakes and then see how long it takes to recover vacuum.
Start checking vacuum lines, 17 year old truck. especially the one going from the PCV to the base of the throttle body at the throttle body, as well as the large line going from the vacuum tee to the cruise control.
Whitelightning
I don't see any vacuum lines running to the brakes. There are lines running to the power steering pump though, I busted out my service manual and it confirms that there were two types, one with vacuum boost and one with hydro boost... guess I got the hydro. Could it be the power steering pump trying to recover pressure causing this? It's really odd... BTW the vacuum tips were helpful anyway b/c although I've been through and replaced them before, when I double checked I found another real brittle one that snapped in my hand, so one less thing to deal with down the road....
Ok you have hydroboast system. key off pump the brakes untill the pedal gets hard and count how many pumps it takes. Could be the "accumulator" is not holding enough pressure. Have you had any problems with fluid loss from the power steering system?
Whitelightning
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