Australian Car Repair Issues? Ask an Auto Mechanic for Answers ASAP
Either you have a faulty spark plug internally, the gaps aren't set correctly, a spark plug was dropped by the installer or in transit, or a faulty ignition lead that you have disturbed upon removal.
I always read the spark plugs resistance with an ohmmeter prior to installation, and also measure the leads resistance.
The trouble with a waste spark system on a V6 is if you have one bad plug or lead you actually lose two cylinders.
Hope this helps.