So one thing that comes to mind is that all that fat you trimmed off, that's all there to keep the meat moist. Now I know there's a LOT of fat on the top of a brisket, but you don't have to trim it all off. Unless I'm trimming for a competition I don't trim very much off. I score it in a diamond pattern to let the smoke through and to let the heat melt it all the way through and then I trim it off AFTER it's done.
Brisket is a tough one. Keep at it. I'd consider foiling it (or paper whatever) a bit earlier as well. Maybe not let it get to 170. I usually foil around 150. As for the probe going in easy, there's easy and there's 'like butter' It took a friend to actually show me the difference. I can tell you I was pulling around 185, 190, 195 and I felt like it 'went in easy'. Now I often don't pull till 200, 205, even 210. Don't be afraid to take it a little bit longer.
Good smokin' luck!
Neil -- "Easy Bake Master"
NB Bandera [gone to heaven...conveniently located in Long Island, NY]
Rebel 23, WSM A, WSM B, UDS, Easy Bake Oven
Pork Pistols BBQ
MOINK...It's what's for linner.