There is more than one way to skin a cat some good and some are bloody horrific, first off cook where the pit wants to run at don't fight the temp embrace it, remember low stress this is supposed to be fun. Keep it simple the meat is the Star not all the Gloopiy Gloope snake oil smeared shakein injected marinated madness.
Follow these rules
BBQ RULES FOR SUCCESS
YOU CAN NOT COOK GREAT BBQ ON A CONSISTENT BASIS BY COOKING TO AN INTERNAL TEMPERATURE OR BY TIME ( XXX MIN PER LB) YOU MUST COOK BY FEEL! For Brisket it must pass the poke test(probe like soft butter in the thickest part of the Flat) Ribs pass the Bend Test, Pork Butts when the bone wiggles loose. These are the only reliable methods to ensure that your cook will be a success. There is one exception to these rules and that is Poultry which must achieve and internal temp of 170 deg in the thickest part of the thigh and 165 in the breast.
Lastly try this exactly
K.I S.S. some of the best brisket you will ever eat! Total cook time including the rest 8 hrs or less. I promise it will be as moist as mornin dew on the lilly, tender as a mothers love, pure beefy smoky goodness.
1 packer 12-15 lb
Trim off the hard fat on each side of the flat thin the fat cap to 1/4"
Mix your Rub
1 part kosher salt 4 parts Med grind Black peppa by volume( this is a true 50/50 BY weight)
apply a coat of rub you need to be able to see the meat through the rub clearly.
Pre heat the pit to 300 deg
place brisket on the pit Fat Cap Down and point to the firebox unless it is a RF cooker then point to away from FB
Maintain pit between 275-325 if cookin on a stick burner
cook Brisket 4 hrs
remove from pit wrap in a single layer of Butcher paper Return to pit Fat cap up.
after 1 hr probe the thicket part of the Flat only! If it isn't *probe tender it will be within 1 hr.
once it is probe tender remove from the pit keep it wrapped in the paper you cooked it in and allow it to rest on your counter until the Internal temp reaches 150 this will take about two hrs.
Don't ever slice more than you can eat big pieces retain moisture and won't dry up on you like slices will.
*PROBE TENDER>This is the feel that is mimicked by cutting room temperature butter with a hot knife, there should be no drag
I never met a Cow that I didn't like with a little Salt & Pepper! Certified PORK-A-HOLIC