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While the High Q grate has gotten excellent reviews, for low and slow cooks I've had the exact same experience as @Black_Badger. I've had some excellent overnight cooks with the stock charcoal grate in the 220 and 230 range where the thermometer didn't budge all night.
"one trick I've found helps in my XLBGE is to clear an area of lump at the front of the firebox before lighting. I like to see about two holes fully clear of obstruction. Since I started doing that I've had more luck keeping the egg lit and settled in on O/N low 7 slow cooks."
XL BGE, Klose BYC, ProQ Excel, Weber Kettle, Firepit, Grand Turbo gasser, and a portable Outdoor Gourmet gasser for tailgating
San Antonio, TX