Small swings are no big deal learn to cook where it wants to run. I think your breaking the cardinal rule of the UDS. Catch your temps on the way up, make small adjustments and wait for the drum to settle in at least 15 min( I wait 20). This is my routine I cook at 300 so you may need to adj you temps a little YMMV. I use about 12-15 briquettes to light the lump in the basket. I let the basket sit about 10 min before loading into the drum. Start with all intakes open as the temp rises I close the first intake at 200 at 250 I close the valve by 1/2 then I leave it alone for 20 min to allow it to settle in. I make the final adj on the valve either open or closed I wait 20 min to allow it to settle.
I'm a Proxy Vegetarian> Cows eat grass & I eat cows.