I don't see #3 being the case here. We have 122 hands on villain; if he's the type to overbet shove scare rivers as a bluff, we'd surely know by now. Literally the only hand I can see doing this as a bluff is T9.

I'd say JJ/44 is in his range somewhere in the region of never. I'd say this isn't ever top pair, because if he overplays it at river to this extent, I don't see why he hasn't raised us earlier. I'd also assume the only made straight draws he has are also flush draws, ie A5cc. I guess he could float Ac5, but it doesn't really matter, it's still beating us.

I think the only hands he has that we beat are T9 (rarely) and 33 (even rarer). I don't take 33 out of his range because I've seen people chasing with it (and getting there) twice in the last week.

This is quite simply nearly always a flush, I'd put it at >90%.

That said, it's an incredibly difficult fold, not one that I think I make very often because I'm a fish with a set.