I don't think Murray has been the issue outside of his hand. I think the run blocking is not as good as it was early in the year. That is not hard to do. Pop in some of the early games like the Texans if you want to see some transcendental run blocking.
Leary got dinged and had a bad couple of games. Free has been on that bad ankle and it got to where he had to sit out. Martin had a bad performance against the Eagles and while improved the next game he still had lost some power. He was back to snapping out of his stance and driving into defenders against Washington. He looks primed for a big game.
They started stacking the box against us in the Rams game -remember how Fisher wasn't going to 'let' us run on his team- but we were able to power through a lot of that anyway early in the season. Between spotty play at the guard spots and RT, we were no longer able to reach some of those cutoffs and defenses were running to the ball on our plays better.
OTOH, we have been much better pass blocking. We were pretty atrocious on stunt, twist, and blitz pickup for much of the year. That came to a head during the Washington and Arizona games. To their credit, they have gotten better. I think I am starting to become a believer in Parnell's pass blocking. The guards have shown much better awareness and they all are much better in unison.