If it is in fact the pump that is causing the problem and not the high pressure line coming out the side of it here is how to replace...
When you go to get a new PS pump (I got mine from Autozone) Rent a pulley puller. Its a couple of bucks and very simple to use. That will get the pulley off. Then when its time to put the pulley back on (with pump bolted into the truck) The PS pump I bought came with a bolt, washer and nut. The bolt threads into the PS pump pulley shaft then you use the nut and washer to press the pulley back on. Like I said, this bolt/washer/nut for reinstalling the pulley SHOULD come with the new pump. Once you see the pump you'll know what I am talking about. One other thing to be sure of, make sure that the pump you get some with a lifetime warrenty. Most places like autozone, pepboys, or one of the checker stores carry lifetime pumps. Also call around and find the lowest price as the places I mentioned gaurantee lowest price. Once you get lowest price go to the store of your choice and usually they will beat that by 5%...save ya a couple of bucks.
Ok the PS is a very simply R&R...
To Remove: Remove belt, remove High Pressure Line from the side, remove rubber reservoir line on the bottom, remove pulley with the rented puller, remove 3 bolts holding pump in and its out.
To reinstall: Bolt pump into truck with 3 bolts, install rubber hose to bottom of pump, install steel HP line into the side of the pump, Press Pulley onto pump using supplied bolt/washer/nut, reinstall belt, fill with fluid.
After you fill it back up with fluid you can do one of two things.
1) Jack up the front of the truck so the wheels are off the ground. Get in and turn the wheel full lock both directions. Then re-check and add fluid accordingly
2) Drive down the street a little bit after filling with fluid once, then re-check and add accordingly. If you do it this way just drive A LITTLE bit so you dont burn up the pump since it may not be full.
Good Luck!! If you have any more questions ask away!