With no read on the HiJack, it is kinda hard to tell you what the correct line of action is for you. But I will say this, calling this turn and folding the river does not make sense. If you are so convinced that you are drawing than fold your 2 outer on the turn. There are many players on party that I would never fold 77 against given the action preflop/postflop on that board, and there are others where I wouldve folded the turn unimproved. But there is not one player on party where I would call down on that board and then fold the river for one more bet in a large pot. I think given that you made it to the river you should call for one more bet, and the next time you are convinced you are trailing go with your read and fold the turn.

EDIT: I just realized that you had 6 outs on the turn, so basically ignore my whole post. That changes everything. I would call the turn, and with no read on the villain I would call the river.