As others have said, ask for the untrimmed flats at costco. At my store, they don't have them out front, you specifically have to ask for them. They are also cryovac'd so they will last longer.
I'd also go with at least a one hour rest, if not two. The hardest part about briskets is knowing when to pull it, especially when you have to factor in that it is going to continue cooking a bit during the rest. There is a small gap between undercooked and overcooked, and it takes practice. I'm still learning also.
“If you don’t know who I am, then maybe your best course would be to tread lightly.”
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