Customer satisfaction at credit unions has slipped in the past year, highlighting their challenge to serve customers who have left banks, according to the most recent report by the American Customer Satisfaction Index (ACSI).

The December satisfaction index for credit unions was 82, a decline of 5.7 points from the reading a year earlier. By comparison, the nation’s largest bank, JPMorgan Chase & Co., had a satisfaction rating of 74, up six points from December 2011.

Customer satisfaction with banks regarding checking, savings and loan services increased nearly 3 points to 77, mostly due to strong and steady client satisfaction for smaller banks, ACSI said.

Wells Fargo & Co. dropped for the first time to No. 2 in the index at 71, a three-point decline.