So, the '07 6MT has two drain plugs for the tranny/front diff. Using a nice Snap-On wrench, I rounded off the 14mm hex head of the rear plug. Had to go buy a Craftsman Bolt-Out set, which worked great.
Since a replacement plug was $6.00 at the dealer and would possibly give me the same problems at the next fluid change, I bought a new 16mm plug from Lowes. This new plug uses a 19mm hex and, when properly torqued, shouldn't be a pain to remove. See the difference below: