My Guru never overshoots on its own, only on windy days, like Wilbur says. Robert has similar good advice for keeping the fan damper on the Guru closed down. I'm running mine right now and the damper is 50% closed, but it's not very windy right now.
I just got the new dual dial door and still learning what the top/bottom combinations are for my usual temps. I've gotten 375F dialed in (pun intended, poochie!), but haven't played around enough at lower temps to figure those out yet. Plus, I've got a leak on the left, rear side of the KK between the lid and bottom, so anything that I learn now will have to be re-learned when I get that corrected.