Does the squeal go away when you are in gear or is it always there? I have a similar problem. I noticed that when I put my truck in gear and press on the gas it goes away, but when I have my foot on the brake or the truck in neutral it comes back. I put some WD40 on the idler pulley just to see if it would go away and it did. Now I just need a weekend and the pulley and I am set.

 

Had my 99 5.9 done at the dealer for 380.00 last October, 1 year 12K mile warranty, and they stated, never had one come back and we have done hundreds. They use a different gasket than the original.

 

same here 5.9l . used grease in a can to find the squeek. changed it the next day. Can't stand the noise(need to hear the pipes.As for your water pump, with the belt off (engine too) grab the fan and see if you can move it up and down or left to right,other than that it should leak or eat the belt up. Changing the pump BITES (had to change one to get out of town before Katrina hit last year.
P.S. you can do it