Can I salvage a brisket that isn't tender enough?

I smoked the flat end of a brisket last night, and thought I had cooked it long enough to fully break down all the connective tissue, but it's still a bit on the tough side.

I cooked it for 4 hours at 185, then 3 hours at 300, rested in a warm oven at 150 for 2 hours.

Internal temperature was 195 when I pulled it off to rest.

Tastes great, but wish it was more tender. Any tips to take it the rest of the way?