1989 Chevy K3500 serpentine belt issue

[fetishersr]

I have a 1989 Chevy K3500 with a 7.4 454, equipt with a serpentine belt that keeps coming off, replaced the waterpump pulley, still throws the belt, all the pullies look like they're in line

 

[zora]

One of the bearings could be dragging but only when hot so hard to determine when not running.