When I first started, I tried every method and technique I could to make good brisket. I tried injecting, I tried brining, I had temp probes in them the whole time and logged the time elapsed/temp in excel to visualize it a bit. I did everything under the sun.
The biggest change I made was tossing all of that out the window and just going by feel. Sure, I will maybe stick a probe in after a few hours to see whats going on in there, but thats it. And that's not always the case. Once I learned how to "feel" the doneness -- I was dominating briskets. If you pick up the brisket and its very flacid, and jiggles if you hit it then it's done. no temp required.
here's what worked for me and made much better brisket (IMO) then any smokehouse I tried in the south bay:
1) get fire going and smoker to temp 275-300.. Depending on timing or laziness I would go as hot as 325 and still deliver delicious tender and juicy brisket; don't buy into that "225 is the only way" crap
2) trim brisket and keep fat cap around 1/4" -- totally up to you
3) generous salt&pepper
4) after 4ish hours wrap in butcher paper and put back into smoker
5a) if using a thermometer to check doneness probe every 45min-hour until probe tender, it could be done in 1 hr, or 3, it's not an exact science
5b) if you don't want to use a thermometer then cook until brisket is limp and jiggly -- this could be an additional 1 hour, or 3 depending on temp and size of the brisket
6a) when done, unwrap the butcher paper a little bit to let the steam out and the temps drop (maybe a few to 10 mins) so it doesn't keep cooking when you re-wrap and rest for 2-4hrs in an insulated cooler
I promise you if you follow this you will create the perfect central texas style brisket.
Some notes:
1 - cooking at higher temps means the "window" for the doneness is much more narrow
2 - cooking at higher temps means that the final finishing temp will probably be 210+. The cooking temp has a direct relationship with finishing temp (e.g, smoking at 225 your finishing temps could be 190, but if you smoke at 300 then it's easily going to be 205+)
3 - once you master "the feel" of a done brisket, you will basically never need a thermometer again.
if you don't believe my method, here are some pics of my beloved bbq off my camera roll. juicy, tender, melt-in-your-mouth, and fucking delicious