I suggest that you join the Lone Star Performance Buick Club and meet some of the members before you go and take your car to anyone unless you want to spend some big bucks on it. It doesn't sound like anything too major is wrong with your car. A buddy system type of diagnosis and parts swapping might save you a bundle in new parts that will not fix the problem. It is amazing how much money some people can throw at these cars and still have them run like dirt.
Good luck.
Good luck.