Ok there are only so many things on the front of the motor that can cause a belt to squeak. You have replaced - belt, tensioner, idler, and water pump with no success. That only leaves the alternator, power steering pump, and A/C (we can assume your crank pulley is not locking up). If the crank pulley was wobbling than you would get signs of side wear on the belt that was causing the noise. It seems to me the next logical step is to - with the truck running and squeaking look and listen to the 3 possible culprits that are left. If you have a bad bearing in one it will definitely be very evident by simply putting a long screw driver against them and putting your ear against the handle.
Also have you removed the belt and started the truck to make sure it isn't something else?
This should not be that hard to figure out - I am not doubting your mechanical ability I just think it is something so obvious you are overlooking it. I, for one, am guilty of that sometimes. We want to assume it is something we have come across in the past and therefore we have our blinders on to everything else. Do you have access to video - if so, post a video of it squeaking maybe one of us will see something out of the ordinary.

M80's seem to work best :)

The alternator HAS been replaced. There is no wear on the side of the belt. I can't post videos. I have a camera that takes videos,but for some reason I can't ever get them to load on my computer. Being the fact that the tensioner can be moved a little by hand, I am thinking of taking a wire of some sort and using it to put pressure on the tensioner by connecting it to the chassis of the truck. I figured that would be a good way to figure out if the new tensioner is malfunctioning.

After reading all the things you have tried, I can only come up with the idea that a pulley is out of alignment. Do you see more wear on one side of the grooves vs. the other? Maybe a mounting bracket is tweaked just a little bit causing excessive wear on one side or the the other? I'm not sure if you have room to run a straight edge across the belt routing using the crank as a baseline and measure back to the 1st groove. Just an idea. Do you know if the truck was ever involved in a front end collision?

After reading through all the responses, I came to the same theroy as Mr_Shamrock. recheck your belt routing.

I came across a similar question on another site I frequent and a few responses were about a very very slight coolant leak that was just getting the belt slippery enough to squeak. That would answer why a new belt fixes it temporarily. It doesn't have to be coolant, but look really good for something seeping.

I'm going to answer two questions with one post here. I havn't seen any coolant or fluids leaking anywhere. The new water pump is on properly,and the lower radiator hoses were replaced when I replaced the pump. I got a good look at things yesterday as I was under the truck changing the oil. As far as the coolant leak would go, that does make sense as to why a new belt fixes it temporarily,but this wasn't the case this time. However the belt hasn't been squeeling much. It seems like first thing in the morning it squeels, and after idling in the driveway for about 30 seconds -1 minute,it goes away. It seems to stay gone until you start the truck up again,but it lasts for a split second and then it's gone. I know that the problem isn't fixed,I'm just saying that it isn't driving me up the wall right now.

As far as a front end collision goes, I'm going to guess and say that it has been in one. When I bought the truck,one of the headlight lenses was missing off of the headlight unit on the drivers side, and neither of the headlights are in properly. It appears that the mounting brackets for them were broken.

Its got to be a bearing issue if it takes a little warm up and then goes away. At the parts store they sell some mechanics stethoscopes to use for situations like these in case it gets worse again.

Insteading of working a little bit and then going fishing for my birthday yesterday like I wanted to, I ended up doing something else. I woke up to the smell of anti freeze in my driveway. Long story short,I spent part of the day replacing the radiator in the truck. That took up most of the day because napa had to get the new radiator from their "warehouse". Anyway,there shouldn't be any coolant leaking now,but after driving the truck 10 miles yesterday, it still squeeled when I started it up. Who knows. I've about given up on it. I don't hear any bearings going bad. I got a good look at things yesterday after I removed the radiator and fan shroud.

I admit that I haven't been around this forum for very long and may not be in a position to give advice. Also those who are trying to help you get this sorted out are obviously very knowledgeable and competent,IMO. In reading through your post, I just wanted to say that I feel your pain and fustration. Have you considered replacing the tensioner and idler with original GM parts? Maybe the after market parts are just not going to cut it in this instance. Just a thought. Good luck and hope you get it sorted out.:)