Charlie, I couldn't agree more w/ pgb ... something is rotten in Pitmaster town. Several (most) of my WSM logs indicate that a WSM, with a full level of KBB, started w/ a modified Minion method should easily cook for 13-15 hours at 225. I have occasionally allowed my coals to "burn out" and seen 17hrs at 225.
Sooooooo, my guess is that the heuristic algorithm in your Pitmaster is poorly designed (not likely or we'd have heard other KettleHeader's comment about it) or your particular unit is faulty. If your Pitmaster "starves" the coal for too long before it initiates the air flow, then you end up with a major cyclic airflow problem (that is; choke the air too low and pump the air(temp) up too high).
My advice, for what it's worth (and really what is ANY advice really worth), "log" some cooks (with or without meat) keeping track of your WSM temps for various damper settings. Once you have confidence in the settings vs temps, you won't need any ATC to allow you time-away-from-the-cook. Or you could just send your pitmaster back to the pitmaster factory