stuttering at high rpms then goes away!
 

I just got my car back aweek ago and had the fuel pulsation damper replaced. When got it back, my idle was messed up. It was around 400-600 rpms.vacuum is now at 14-16 instead of usual 16-18. I had to adjust my idle valve and got my rpms up to 800-900. but vacuum is still at 16. anyways when I first start up car and drive it slow until the temp guage goes up to normal, about 10 min.later , i'll get on it and it will start to stutter from 6,000 until redline, it would hit 13 lbs of boost and hold it,but it feel like i'm loosing power. 3 min later try it again one stutter and hauls ass. Still getting little back fire from time. Is this normal, maybe it needs to warm up longer or is it just cleaning itself out.