I would raise 4th. Only 1 other 8 left and this will test him. If he raises then you can start worrying about the trips. Ks are strong here and your hand is very live.

At 5th, his bet is hard to interpret. I definitely call. I suspect Ks up could stand up but a flush is likely a winner. (If you had raised at 4th, then you should probably only call).

I agree with calling 6th.

Here's the problem on the River. Had you raised 4th, you would have a better feel for trip 8s. As it is though, because there's already an 8 gone, a Raise is tempting. Indeed, the flush is what we were waiting for.

Cheers,

PG