This may not be as applicable for the newer LS engines, but for SBC-powered trucks here is a quick fix for the annoying squeaky belt:

Assuming the belt is in good condition and all the pulleys are aligned correctly, the belt squeaks because it got some oil on it. It needs to be cleaned and the squeaks will go away.

1. remove belt and place in bucket of soapy water for a few hours. I used a high concentration of dish soap.

2. spray down all pulleys with brake cleaner several times.

3. dry the belt and re-install

4. enjoy driving with no squeaks until oil leaks onto it again in 6 months or so...

Hope this helps!

REZ