I took the car in yesterday to get it looked at by a dealer. The fee was pretty reasonable ( $100 ). It sounds like they hooked up some electronics and took it for a test drive.

The verdict was that the EGR ports were probably clogged. I didn't think of that because I cleaned them out 2 years ago, but I really don't know how long it takes to get clogged up again. When I did it two years ago, I think it was because of a check engine light and a code that directly pointed me to that issue.

I get the car back today and I will go through the EGR cleaning again. Hopefully all will be well again.