special tool not needed
Two ways to get the pulley off; remove the fan with the pump on the engine, then (if you have one at home) get your power chisel gun out and use a 6" stud pounder or dull bladed chisel against the nut face. you'll have to "lock" the pulley in place; I used a strap wrench from Autozone to keep it in place.
Second, remove the water pump with the fan in place. Then unbolt the fan, and take the pump ass'y to a local shop, who can remove it there with the air chisel method or big ass wrench! I would recommend you have the new pump with you so they can transfer the pulley right there. Good Luck!
A Chilton's or Haynes manual (I have both for my 01 Yukon) will spell out the steps involved, but it' pretty straightforward if your'e handy with tools.