Just a thought, changing plugs and not wires is asking for trouble.

I put in 12 plugs and wires at 90,000 with my Graphite limited and the difference was very surprising to me.
(I should note that I had intermittent O2 sensor and misfire sensor codes for about six months leading up to new plugs, once I changed plugs and wires, all the codes went away and the car ran better.
I can't say I had any complaints - its just that powering out of a curve was WAY more fun after the change. My current SE is at 73,000 and I'm am strongly considering changing plugs and wires this summer - but its 18F here in DFW today - so the car can SIT.)