I have had a loud belt squeak going on for a while now. I had the belt replaced about 6 months ago. I am able to hold a soap bar to it and it stops for my drive, as soon as I re-start car the sound is back. I repeat the soap trick again and again and again... any idea what it could be?
More than likely, the tensioner pulley spring is weak. If, when you are running the truck, you see the tensioner flex a lot during operation (belt easily tries to straighten out), then the spring may be weak. Also, a lot of GM vehicles have a gauge. Look at where the pivot is for the tensioner pulley. Between the arm and the body, there will be an arrow on one side and a bracket showing the extent of movement on the other. If the arrow is close or outside of the bracket, the spring is weak and the tensioner must be replaced.
The soap on the belt will cause the belt to "slip quietly" – rather than stopping the slipping. Belt slippage is almost always due to either a damaged belt or low belt tension. With a newish serpentine belt this means that the problem is almost certainly the belt tensioner as there isn't another adjustment.
Another possibility is the wrong length belt was installed when it was replaced. Go to a parts store and get the part number, which is usually the belt width and length. If you want to make sure ask them to pull the belt and look at the number printed on it. Look on your invoice from when the belt was replaced, or on the belt to see if the number is there, and see if it matches what is specified for the truck, engine size and options. If too long a belt was installed the tensioner would not be able to take up the additional slack once it wears in and stretched.