I played around with some briskets ( whole packers ) yesterday and decided to try the higher temperature. I cooked them between 300-325 degrees and around 6 hours they were between 200-210 degrees, but they were not tender with a butter knife test so I backed the temp down to 215 and left them on another 5 hours and they were better but still nowhere close to a 12-14 hour slow cook. What did I do wrong, if anything?