2000 Chrysler Cirrus Check Engine Light Serpentine Belt Change and now shifting stalling problems?

Check for vacuum hose leaks under the hood, causing the car to run too rich. The Mechanic may have knocked a hose loose or leaned on a hose causing a crack at the connectors while he was changing the belt. It's not difficult to replace an air hose. Take the old hose to a shop and match it up with a new hose. You might have to cut it to fit. If it has a 90 degree bend in the hose, you might just be better off going to a dealer and getting an original replacement with the same 90 degree bend. Be sure and buy band new hose connectors while you are there. Also, Autozone might be able to match the hose up with another off the shelf if you bring it in. They can cut it to the correct length, if they can just match the hose bend with another hose.