Fans headed to southern Virginia for this weekend’s NASCAR Sprint Cup and Camping World Truck Series races at Martinsville Speedway will see a post-season twin bill as the 2016 schedule enters its final month.  Six title contenders remain in the inaugural Truck Series Chase heading into Saturday’s Texas Roadhouse 200 led by top-seeded rookie William Byron.  Also still on The Chase Grid are Christopher Bell, Timothy Peters, Ben Kennedy, Johnny Sauter and Matt Crafton … In the Sprint Cup Series, the title field is down to eight for the final short-track race of the 2016 season, Sunday’s Goody’s Fast Relief 500.  Kyle Busch, the Number-1 seed in this year’s Chase, is looking for a season sweep on the Virginia half-mile after winning the year’s first stop there in early April.  Denny Hamlin’s the last driver to win both races in a single season, doing so in 2010.