I'd assume your rotating your players effectively? When I see a linebacker or a linemen huffing and puffing, I either run the ball right at them or attack the linebacker (preferably a drag or streak on him).
As for running mechanics, are you using the 'get skinny' mechanic. It's RB on xbox and it basically makes the running back dip his shoulder to get between linemen. It's the difference between a 0 yard gain on 3rd down and a two yard gain on 3rd down for the first.
Also, after (or during playing if you can) look to see who got beat on a block and who beat them. Rating play a larger factor on the sliders. If you have a TE that can't block (i.e Antonio Gates 65 RBK) he won't be able to seal the edge. Respectively, if a center can't RBK then there will be constant pressure up the gut.
If you REALLY need to get that short yardage, I'd just sub in tackles for TEs