Your Automatic tensioner could be worn out.
Did the last shop have it off and not install it properly?
Your local shop can find the tension torque specs.
-Half inch torque wrench, with a 3/8 reducer. put it in the tensioner slot, see what kind of torque it takes to move that baby, should tell you if its worn out or not.
Edit: from identifix
Inspect indicator marks and replace belt if mark is not between reference marks on tensioner. So check for those marks on the tensioner, make sure there inbetween.
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