Hi all, my girlfriend has a 2000 Grand Prix non SC 3800 with 155651 miles on it, when cold idles smooth unless you rev to 4000 rpm starts cutting out then as soon as it has run a few minutes the rpm starts bouncing around and it dies then wont start again till it has cooled for several hours. It had codes p0102, p0300 and p0420. Checked fuel pressure was 43 book stated should be 48-55 so replaced fuel pump. No change. Replaced coil packs and plug wires, plugs are fairly new. No change. Replaced ICM. No change. Replaced MAF. Cleared codes. No change. Checked vacuum lines, appear to be fine. No longer getting any codes but it wont stay running very long. I dont have much experience with these as I am old school shade tree mechanic. Any help would be much appreciated.