From the title you said middle set but I dont see the your hand on the post so assuming you had Pocket 5s right?

As played I think the math tells you to call, the problem is that villain's check on the flop after he cbets wide is usually a draw, the flush gets there on the turn and some str8s get there on the river.  I don't think the villain is floating this turn to shove bluff river most of the time, and doubt he plays 1 or 2 pair hands this passively on the flop and turn and then so agressively on the river.  He might have a set of 3s or 2 pair with a 3 that he hit on the river but highly unlikely IMO.  Even though almost half my stack is in there I am folding.  I just don see him bluffing with 1 pair or having 2 pair or worse sets and playing the hand like this

I do get that this could be a bluff but dont think its worth it vs elimination, The villain knows he is putting you at a super tough decision considering ICM with the other 2 stacks being shorter, my advice is to try to stay away from this situations unless you have premiums and dance with the other 2.  I am ok if you want to set mine but then play it faster with a larger bet on the turn or a donk bet on the flop. If you want to go for max value like you did here you are going to have to call that river bet. 

I definitely think this is a call. I don't see a guy that cbets 90%, checking back his draws. He's pretty aggro from what you said. I really don't know what he checks back..  A2 with Ace of hearts is probably something he'd call the turn with.. maybe just A2 no heart if he thinks you are bluffing and Hero calls a lot..  He could x/b the last 5 in the deck.. a hand like 53s..   Doubt he has JJ.. I think he cbets that 100% of the time on this flop.. He probably x/b with a bottom pair/second pair hand.. highly doubt he x/b a draw unless it's a hand like 76.   He could float the turn with Ax.. A5.. he could be turning a hand like T9 into a bluff, maybe he x/b because he had backdoor draws, he hit his backdoor draw, and decides to call with a straight draw because of the 3flush.. turns it into a bluff OTR because of your sizing maybe..

seems fine as played (assuming you called river), as long as you arent purely set mining.

I think this actually may be a fold pre. We may be ahead of his range. We may have 60% equity vs. his 3betting range, but we need to be able to “realize our equity.” (funny phrase :)) That means we usually need to be IP. It’s going to be difficult to do anything other than set mine vs an aggressive villain like this with 55. If it’s like 88-TT, you could call (or 4b/c like 4b smallish to induce a 5b jam bluff) and it would be a lot easier to get to showdown without a HUGE guessing game because sometimes there will be NO overcards.. With 55s, it’s like 95% of the time there will be an overcard. I’m not sure if you know about the 20 to 1 rule. You need to be able to win 20X the bet size you are going to call. (That includes the villains stack+current pot). It’s going to cost you 2,044 chips to call. You need 20X that. That makes it 40,880 chips needed to win. The good thing is that you don’t always need 20:1. It just depends on your implied odds vs. the villain. If you think you can get his chips easily (if he’s as aggro as portrayed, we will be able to get them easily), you can lower it.. I’ve seen as low as 15:1.. That’s 30,660. The effective stacks are definitely big enough to warrant a call using that measure. The 15:1 / 20:1 rule is basically just if you are calling to purely set mine. If you were in position, you don’t always need 20:1 because you will be able to float a lot of flops, and bet the turn to take away the pot.

I also didn’t mention this in my first post, but he could also check back AA with the A of hearts. or KK with Kh. What did he end up having?

wow A3hh is a really sick checkback if he was truly c betting 90% and it didnt jus feel like he was c betting 90%, also if you had just been folding a lot of hands to him and then call all of a sudden, i do expect him to check back a lot of draws here, as your hand is usually nutted and he doesnt want to get check raised…like you were trying to do

i def like folding pre oop here vs super aggro villian, as played i like leading flop here, if we lead flop it gives him a chance to spazz 100% of his range if he feels he can pressure you, and i find most people are prone to raising donk bets (myself included) deep in tourneys as they are just so fishy