Should I call this raise on the river?

Hi all,

I was playing some $2/$5 last night at my local casino.

Action folded to the button - a regular loose passive low stakes superstar - who limped for $5, I look down at A♥Q♥ and make it $30, he calls. Effective stacks are around $900; 180bbs.

The flop comes A♣T♥9♥ - all well and good; I bet $25 and he calls.

The turn brings A♣T♥9♥8♥ - bingo! I bet $75 and he calls.

The river brings A♣T♥9♥8♥9♣. I bet $150, he gives a speech asking if I have a flush etc and then raises to $375.

Well dangit! Can I find the fold here? How does he hit a set at any point and not raise earlier in the hand? 98s was a hand that came to mind that he could have. I realized that there are very few combos of flushes that he can have here after limping and calling a raise - perhaps only KJs, 76s, 65s, 54s. Is he really going to slow play those on the turn and raise the river? Perhaps with exactly 76s for the straight flush. Am I too high in my range to fold, especially as there's a possibility he's raising for value witha worse flush?

Hero...?