Well, Tretter's big skill last year (according to Larry McCarren) was that he was very athletic, good at "reach blocks" and getting out on linebackers. He is a natural center, although a bit light in the butt. Guy was a TE for two years of college. I'm reminded of Flanagan, another lean/tallish center who did some rough time at LT.

Maybe Tretter has put on some weight and can play guard.