I don't see how you want a 1st year player released, after getting a 3.6 average. I know RBs tend to just run it good right away, but as with all rookies, some need some time to develop. Going from a 3.6 avg to a 5.5 one seems like making progress to me, even if you're not always running the ball.
Grant is in his first complete year as a starter aswell. They're acually able to gameplan against him now, wich they weren't able to do last year. He s in his third year as a pro though, but I give him the benefit of the doubt. He will have to step it up next year though, because there's no point of waiting even longer if he can't get it done by then.