I had the exact same issues you are having, until I figured something out. I had already moved on from these sliders to an All-Madden set thinking that may have been the problem, but I gave them another try last night and had dramatically different results.
The one big thing I did differently, was I called my own plays instead of going off of the coaches suggestions.
(Suggested by Armor earlier in the thread, which set off a light bulb for me.) I chose the formation, I chose the play, and I ran that offensive/defensive play. Before I had been using the coach's suggestions and didn't even pay attention that the suggested play was the same run play from the same formation, over and over and over again. The AI was more or less exploiting itself, and I wasn't aware.
I had been averaging 265 yards a game with Kenyan Drake through 5 games. Last night I played against the Bills in my CFM, an Kenyan Drake ran for 85ish yards on 26 carries. Much much much tougher to run last night with calling my own plays and not exploiting the AI.
On defense, I did a good job on Shady McCoy. He did end up with 250+ rushing yards, but that was only because at the end of the game
I got out of position on a couple tackles and he broke a 60+ yard run and an 80+ yard run. If you take those out of it, he ends up with just over 100 yards.
Another thing, is make sure to use the auto-subs suggested. I hadn't been doing this, and Drake very rarely came out. Last night my backup ended up with 7 or 8 carries, which helped to lower Drake's overall production to a more realistic level.
Just a couple suggestions to try out.
After altering the way I was playing the game, the slider set worked much better and provided a much better experience. Give it a try and let us know how it's going. One thing I had noticed was that the AI was breaking big runs on me in previous games on runs to the outside. With calling my own formations/plays, I was able to counter this much better than using the coach suggestions. Also, on offense, I was able to make sure I wasn't accidentally exploiting the AI without realizing it by using the coach's suggestions and running the same play for 8-10+ yards each time.