I like a check back otf. You're 3rd in chips, and like you said, you've been able to chip up fairly easily.
Let's say it was 8,000 ante. So otf, there's 400,000 in the pot, and you have 1,632,000 behind. This flop is gross, even though you have top top. What are you going to do if you bet and turn is a spade, 6, 7, 8, J, Q, or K. What is that, 27 cards? You could get bluffed off best hand, you could be drawing dead, etc.
Let's say you check behind, the 2 hits, and he bets 300,000. You call. Pot is now 1,000,000 and you have 1,320,000 behind. River is the king. You can fold and still have like 16.5 bbs left.
I think you need to pot control here and don't want to play a big pot vs chip leader w a one pair hand. Even if he bluffed you off best hand (say he had Js8s), you'll be able to find better spots later on and chip up in the meantime.