serpentine belt falls off and caravan jerks

I bought a 94 dodge caravan last year. So every time it rains the serpentine belt comes off. I replace the belt twice also when I go to the speed of 45 and
55 the caravan jerks and then it stops when I get to 60 mph. Can anybody give me some suggestions.:confused:
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" snipped-for-privacy@yahoo.co"
Profile: http://cardealerforums.com/member.php?useride3

The belt tensioner may be bad causing a slight tilt on the belt, rain hits it and it slides off.
Glenn Beasley Chrysler Tech
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