One thing to check is the crankshaft harmonic balancer AKA the composite rubber/steel crankshaft pulley at the front end of the crankshaft.There was a spate of these failing on the v6 motors as the rubber parted company with steel. If this happens at speed the timing chain cover and sump castings can be damaged by flying debris. Yours may have been replaced but worth checking- lots of posts on this if you do a search. when it comes to a plug change remember you have 12 twin plug system.
Welcome to the club ---particularly like your wheels