The running game is struggling so much because
1) There is no Dez Bryant to stretch the field
2) Teams know there is no downfield threat, so they are free to clog up the running lanes
3) We miss Callahan more than expected. The O line is giving decent time for passing, but they do not look like the O-line of last year. Some of that could also be attributed to not having Murray and also to not having Dez to stretch the field though.
The OL has been severely overrated, this is what they really are... They can be really good at times, even dominant for stretches, but they were even inconsistent last season, as was the running game later in the season... Romo makes them look a little better than they are at times... Romo also made Murray look better than he was, because Murray doesn't rack up all those yards, if Romo doesn't keep the chains moving during those times when he was struggling to gain yards...
We just need to get Romo back... It helped to have a really good ground game, but when you have Romo, Dez, and Witten, you'll be fine, even with a mediocre running game. We can score enough points on offense, it's the defense that needs to be more consistent and maybe generate freakin' turnover.