This thought crossed my mind when I saw all of his gaudy yards and carries, but I don't think this will be an issue at all...at least not in college.
He's at the age where his body still recovers at the speed of light, and I just don't see him running out of gas while in college. Now, his career after college (assuming he makes it to the NFL) is another question all together.
Some of the other guys on here might have a little bit better idea about this than I do, but I'm not even positive that he ends up being strictly a RB. He has shown that he has the ability to run the rock with the best of them, but his frame is built more like an H-Back in my mind...he really could end up being an extremely versatile player.