It's not a question of May's "ticker" nor being "timid". Nearly every player who does an ACL is timid in his/her first few games back (sometime longer) as sub-consciously they are not sure if the repaired joint will not go again when they put any pressure on it.
I've seen plenty of players like that at the Roosters. JWH, who admittedly is a front rower, took a while to get back to his best running the ball after he came back from his ACL rupture, and Jared is not timid by any stretch of the imagination. Its not straight running that is the issue, it's when they need to use ay lateral movement it can be noticeable. Some players though can wind u losing a step or two pace wise - Ryan Cross did both his ACLs in a 2 year period and he was never quite the same afterwards.
It will just be until he feels that the joint is fine before he might get back to his pre-injury form. That is more emotive and sub-conscious than a conscious thing.