Engine miss/skip when warm and driving.

I had a similar issue with my '04 Tbird. Sometimes came up with a misfire code, but mostly not. When a tune-up didnt fix it, and after much frustraion, it turns out there is a service bulletin on the ignition coils, something about leaky gaskets allowing moisture in to fail the coils. Dealer should replaceme up to 10yrs/100k miles (from what I remember). Search the net for Bulletin No: CSP 07M07

Check ign. coils you are right at the mileage where they start failing. They are warr. for 100K miles and can be checked by reading computer codes.