MrGC, had you changed the spark plugs before your #4 & #5 failures? Normal maintenance calls for their replacement at the 100k mile service.
Having read on the net of the COP and possible ECM failures, I changed my plugs a little early. The electrode gap was larger than specified. That would cause the plug to have to build to a higher voltage before the spark would jump the gap. Rounded electrodes due to wear also make the spark reluctant to jump, so the voltage again is higher. If it gets high enough, it can jump through the COP boot to the cylinder head. That causes the misfire code, and can allow unburned fuel into the catalytic converter, which will melt the gizzards. Not good, and expensive to repair.
If you haven't changed the remaining 4 plugs, do so at your earliest opportunity.

tom