Bark looks really nice......
If I'm remembering, you got one new, right?
A new model will take a few times to get some build up on the lip of the bowl & the inside rim of the lid & it will then seal better & cook a bit more consistently.....suggest not cleaning those surfaces, or very light cleaning if you must.....
As for temps, 240~270 is almost no swing at all....think of it......as a section of fuel (briquettes, lump, wood) catches, the temp will go up some.....as those burn thru, it will drop a little, and then the next burn area will begin with a minor upswing.......75 ~100 degrees is a swing that you might want to do something about......
Here's a set for a brisket cook on an older 26".......daisy wheel vents on the underside (just like the lid vent on all Webers)
This set ran about 7~8 hours between, yep, you guessed it, 240 & 270........all vents open (the lid is always all open to not choke the airflow & allow for as much exhaust as possible....crimping down
can lead to stalled stale smoke in the cook chamber) no vent adjustments for 11 hours....the kettle does the work, just like it was designed to operate..........
Therm is at about 260 here....
Then fuel was added to finish up.......
It's running at night, by itself, without me checking on it, so temp spikes do what they will with no help or interference from me or the dogs (who help extensively with all BBQ's)