i'm cahsing down the same problem.

So far diagnosis and help from FTE members has gotten me to either the map sensor or the fuel pressure regulator.

Check to see if it has any thing to do with vacuum. You're getting a lot of vacuum at idle, and at higher rpm low throttle situations. Those are the times i experience the mis-fire.

Try unplugging the fuel pressure regulator and see if that does anything. Silver streak suggested this to me and the mis fire dissapeared completely, so i've gotta check out that regulator.