I changed the plugs in my 04 GTP w/ 98k. I put in autolite platinum 605's. At an idle it used to have a periodic miss which annoyed me, it's gone not, great. During normal driving it's nice and smooth again, great. But now if I put a load on it to pass somebody or going up a decent hill, it boggs down skips and misses. Any clues as to what would cause this? the one heat level cooler should do that right? It's bone stock.