Both Goodyear as well as Gates are carrying special field fix kits that address the serpentine belt jumping issue that is so familiar with Chrysler minvans. Call your local distributor and ask for the double ribbed belt kit for your van. This special belt has ribbs on both sides of the belt so that when it is installed with a new tensioner and grooved idler, it LOCKS the belt into place and it will not come off even if you spray it with a fire hose!!!
Don't take my word for it, Check it out for yourself. You will not be disappointed.