Gravely 54" Zero Turn deck belt turning onto side.

I have a Gravely ZT54XL mower (Model 915188, Serial # 045147).  I keep breaking belts because between the engine driven electric clutch pulley & the 2 double flanged flat faced idler pulleys the deck belt keeps turning onto its side.  There is a significant difference between the height of the clutch pulley & the idler pulleys so the back of the v-belt leaving & entering its respective idler pulley does so at a significant angle & rides onto the shoulder edge of this pulley which allows it to turn onto its side.  I have replaced the idler pulleys, the tensioner spring, several belts & keep having the same issue.  All spindle bearings are tight, everything turns freely with zero slop or movement.  I have tried positioning the 2 idler pulley belt guide fingers in different positions to stop this problem with no luck.  Any suggestions?