Good post. I also think it is multiple, smaller, issues and not just 1 major issue. Starting on the OL, the 2 guards specifically are getting beat on inside runs... some of that is due to anticipation by the defense, IMO. I personally believe that there's more yardage to be had outside the tackles, but there's issues there too. Having some lighter, quicker linemen that can get outside quickly on blocks would help, but that ain't happening this year. Danny Lewis Jr coming back soon would help however, IMO.
On the backs, as mentioned by many, Jam is too slow to get going and to tentative at times. His vision isn't great and he sometimes runs with his head down, which sure doesn't help. I like what Hill adds, but he's still a liability as a blocker.
Thirdly, the play calling... I don't mind the run calls, but at times, the calls have been way too predictable. And predictable is fine when it works, but when you're gaining a yard up the middle every time on 1st down, mixing it up some would be better. Still, much of the passing game with Simpson is based off play action, so the threat needs to be there. I'd personally like to see a little more off tackle stuff. And it's obvious that Grubb is trying hard to find other ways to get "ground yards" with some of the stuff he's doing, but too much of it is borderline reckless with the trick plays. And if you're gonna run Wildcat, let Bernard take the snap, not Jam. At least Bernard has better vision, feel, and has shown the ability to make chicken salad out of chicken shit when the blocking breaks down. Oh, and he can also throw it, which could come in handy. Also, more speed sweeps with the WR's. Lastly, I haven't bothered to chart it, but my eyes tell me the offense runs much better (yardage and first downs) when they incorporate more pre snap motion. Keep that up and do it more on the run plays.