A tip on using the Guru - your top hat damper should just be barely off the seat, regardless of your desired grill temp. Let the Guru fan force the air through instead of the usual nature draw. With that 20 cfm fan, you shouldn't have any problems moving air through that tiny gap. However, on a windy day - there's an adjustable damper in the nozzle of the fan, close that down to almost closed if it's really windy out; otherwise, when the fan's not running, the wind blowing across the top hat will vacuum drag too much air into the KK and your temperature will go up above your setpoint. The Guru can't bring the temp back down, it will just stop running; you'll just have to close it down and wait for the temps to decay back naturally, which can take a while depending on how much above the setpoint the temps get and for how long.
Learned this one the hard way - on a very windy day, the grill temp went almost 50F above my setpoint before I noticed. Cook was over before it came back down to where I'd set the Guru. Didn't ruin the cook (pork butt), but it did cook faster than I was planning. Moral of the story - while the Guru makes long cooks easier, it isn't foolproof, as this Fool found out!!