Thanks for all the awesome comments and advice.
To answer the questions posed:
I'm cooking on Kingsford Blue. I have used lump before in my offset and like it, but think that while learning how my new baby runs, I'll be sticking with it for consistency's sake.
The temperature variations I was getting were between 250-315 in the span of 15 mins, and 325-385 in 20 mins or so. I wasn't happy with that. I think I know why now though...
Long term I'm primarily going to be trying to cruise around 225. I built this UDS mostly with dreams of delicious shoulders dancing through my head. They were just a royal pain to do on my silver smoker, though I've done it for years. Usually do whole hogs on rebar over makeshift cinder block pits with roofing metal as a lid... So don't get me wrong, this is a major improvement
I think I'm going to keep cooking the chickens on my offset in the long run, but I digress.
So I went to the local hardware store tonight and picked up some 2 inch pipe and devised an experiment.
First I added a smokestack: 12" of 2" pipe. I know this is probably too long, but my plan was to start long and just shorten as necessary.
Then I lit 12 briquettes of Kingsford blue, put in about 8 pounds more into my basket, a few lumps of hickory and then added the lit coals to the center of the basket. I got out a pen and paper and began to systematically record the temp and valve settings at 10 minute intervals. Into the drum the basket then went with one intake uncapped and the ball valve open. I capped at 200, then throttled it back to 1/2 on the ball valve at 200. It climbed to 225 and dropped to 213, where it stayed rock solid for 30 mins. What I learned was that with some very fine adjustments between 75% open on the ball valve and 90% will vary my temp from 215-240, but it seems to be leveling out, and is certainly much easier to control. I've been holding between 220-230 for two hours now though, with only extremely small adjustments to the valve. I'm going to just let it go all night at this point and see where I am first thing in the AM.
What I've learned:
1. Patience is key- I think I was overreacting to changes
2. The chimney seems to help a lot. I mean it was dramatic. I may shorten it from 12 inches, many people recommend shorter, but I may just roll with this, it seems to work
3. There's a sweet spot between 75% and 90% on the ball valve, the temp will vary between 210 at 75% and 250 at 90%. Extremely small adjustments in there let me dial the temp in.
4. The brethren are AWESOME. Thanks for all your input. And to think I've been doing this alone for all these years...