I did the same thing with my first couple of briskets. Today I had my first successful cook in my drum. I took bludawg's advice and cooked it hot and fast. Temps were around285-300 for the cook. I went four hours and the color was nice so I wrapped in butcher paper and threw it back on. Checked about and hour later when temps were in the 190's. probed it, still tough, gave it 30 minutes checked again, boom, probed like butter. Pulled it let it rest 20 minutes, then wrapped in foil and coolered for a couple hours. It was awesome.
I owe my success to bludawg. I always see him posting this method so I went with it and the results were awesome.