Ok so I have a 2002 4WD Xterra with about 130k on it.

First, the ABS light has been on for about 8 years - faulty sensor - but never really had any brake problems.

OK now, on occasion - probably about 10% of the time - I'll start up the X, and start driving slowly like in a parking lot or in my neighborhood. (1) I'll hear a clicking noise coming from the dash, (2) The ABS light will turn OFF, (3) The brakes kind of work, they're kind of grindy, the pedal feels funny like it doesn't want to push down, I lose that nice hydraulic feeling in it.

This will last for between 10 - 60 seconds before it snaps back into place (brake works perfect, clicking noise goes away and the ABS light comes back ON as usual) and everything works fine for the rest of the drive.

I can also get it to stop by hitting the gas punching it into the next gear, but obviously I can't always do that if I'm in a shopping plaza or picking up my kid from school.

Anyone have any idea what's happening here?

Thanks,
Alan

The sound seems like that's the brake light relay clicking on/off. At the same time it seems like you loose power brakes based on your description of the hydraulic feeling.

Maybe ABS control module. See this description of how the ABS system works http://auto.howstuffworks.com/auto-parts/brakes/brake-types/anti-lock-brake1.htm loosing that hydraulic feeling seems like the control module is isolating all brakes in blocking mode.

This may be one of those repairs to take to a specialist.