Have you replaced the serpentine belt? They do wear out especially if you had a bad alternator pulley.
A bad alternator pulley also can severally wear out and weaken the tensioner spring for the serpentine belt tensioner due to high cyclic bouncing; so you should consider replacing the tensioner pulley as well.
IDParts.com sales a nice kit with a new belt, tensioner pulley, and idler pulleys:
LINK>
Serpentine Belt Kit (Liberty CRD)
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