Swapped the serpentine belt and the idler pulley out today. I replaced the idler pulley once before with a Dayco. It's been howling on and off for a week or so. I swapped it for a Gates pulley. The new belt is also Gates. I got a belt for a van, it's about 1/4" longer than a truck belt. I can't see that making much difference, but technically it's what should go on it with the van pump. I've never replaced the belt before and while it looked fine I have no idea how old it is, so figured I may as well swap it.