Doesn't do it all the time, but seems to be getting more pronounced. Any ideas?

 

Out of balance wheels? Out of round drums?

 

Warped rotor if you have rear discs, or a leaky axle seal can sometimes make your brakes grabby

 

Wow, I'm an automotive bum these days! I can't believe I originally posted this in March of '10.

Problem solved (almost) - the p/o put Autozone lifetime pads on the front of the truck, and the rotors were shot. I've driven for months like that, but did the brakes today.

Turns out the rears are fine. Almost no wear. I did the '03 upgrade on the front as the truck has 17" wheels, what a difference! Bosch premium rotors, Wagner pads and "reman" caliper brackets from O'Reilley auto parts. Total bill, $390.

Now to replace the shocks. They are the original shocks and so shot that the rear end bounced on braking because of totally expired front rotors and pads. My wife says she'll ride in the truck again, I'm glad. Her little Infinity coupe has small seats for my frame.