I know this thread is sorta old at this point, so it might not help the original poster, but it could help someone, so I'm adding this.
I have an '05 that had the same problems. I had power issues, wouldn't hold idle unless it got hot, needed to use the choke all the time, etc.
Turns out I had a bit of a head gasket leak! As things heated up, stuff would expand and mostly fix it, but it wouldn't quite live up to its potential.
Changed the head gasket (and cleaned everything in there while I had it open) and voila! Works like a charm! Best it's ever ran!
In fact, it worked so well that the extra power made the clutch start slipping and I had to replace my plates and springs!
Hope this helps someone.