Coffee's impressive runs disappeared as soon as the games started counting. Maybe he's being coached to run north/south, no fancy stuff, but he seems to seek the pile instead of the daylight.
As I recall it, Coffee came in as a rookie promising to seek out contact and punish tacklers. He said it would be easy on this level, just like in college.
But I think he's found out that a high running RB trying to challenge NFL linebackers is looking for big trouble. The 49ers O line isn't the huge Alabama O line, and the tacklers aren't college players, they're assassins hunting heads.
Maybe too early to give up on him, but DEFINITELY time to draft some competition in April. Say 3rd round, where the Jets found Shonn Greene.