01 GTP is missing in upper rev range. The check engine light came on and it show po300. Had it further diagnose and it show I had a bad coil #1 and #4. Had it replace. Ran good for awhile until I started to get on it and it started acting up again. Had it diagnose and it showed po300 misfire for #1 and #4 in the history but no check engine light came on. Need help please.