I'm not folding here. With 2600 in the pot, he bets out 1800 and has 1200 behind. So I'm looking at it as calling 3000 into a 5600 pot. Almost 2 to 1 on your money. His line is a little scary, but there are too many hands he could do this with other than a 10 or boat for me to fold KK heads up. This is the type of fold that I only make with a great read, usually in live play- even then, the betting pattern alone probably wouldn't convince me to fold.