By Jared Turner Just when it seemed that Martin Truex Jr. might be slightly vulnerable in his pursuit of his first Monster Energy NASCAR Cup Series championship, the Furniture Row Racing driver threw cold water on any such notion with a convincing victory in the Bank of America 500. His berth in the Round of 8 now 100 percent secure, Truex can take the next two weekends and simply focus on piling up even more playoffs points for the next round — which he’s already poised to begin with a substantial lead, thanks to his numerous race wins and stage wins this…