Look at this quote from Von Miller:
Some of the tendencies that we had maybe thought of throughout the week, they were a little bit different, so we kind of understood, just throughout the game, that if they were in certain formations, if they were in certain personnel groups, this is what they were doing. Early on in the game, we were still trying to figure it out, but as we got through the game, and you started to see plays repeat itself, we were able to kind of settle down and see the same plays over and over again, and, like I said, make the plays when we had to.
Seems to me this is the reason we come out guns blazing then stall in the second half. Coming from the horses mouth the same plays are repeated over and over so the opposing team adjusts and stops the offense.