I typically leave the vents wide open until around 200, then close all 3 bottom vents between 1/2-3/4 shut and leave the top wide open until it comes up to temp. Once I hit about 240 or so, I shut the top vent about 1/2 way and that usually settles in around 250...ish. Then I just adjust vents as needed, which isn't much.
Are you using lump or briquettes? I've always used KBB until recently switching to RO lump, and I've noticed that I do have to work harder to keep the temps under 280. Still learning this. That being said, the difference between 250 and 275 is not all that great...I'd be more concerned if you were running at 300+.
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