10/20 Live. River raise... WTF?!

[KarlSpakler]

10/20 Commerce.

Folded around to hijack who open limps. I raise in CO with A [img]/images/graemlins/spade.gif[/img] J [img]/images/graemlins/spade.gif[/img] to $100. Button folds. SB asks how much I have (set miner), I have 4K. He has 2.5K and calls. Folded to limper who also calls with about $500 behind.

Flop:

Q [img]/images/graemlins/heart.gif[/img] T [img]/images/graemlins/spade.gif[/img] 5 [img]/images/graemlins/club.gif[/img]

Checked to me. The SB seems anxious and I read him for strong on this flop. I check behind.

Turn:

A [img]/images/graemlins/diamond.gif[/img]

Both opponents seem to like this card. Checked to me again. I check behind again, planning to control the pot size and call a reasonable/pot bet on the river.

River:

A [img]/images/graemlins/heart.gif[/img]

SB checks, hijack pushes for $510 into $320 pot. This is not the sort of bet I planned on calling. As I consider my action, the hijack's friend on the rail wants to see his cards. When he shows them to him, I see them also. He has A7o. My J plays. I call.

SB, who I had since dismissed, now raises $700 more.

I am so stunned and confused by this, I forget my flop read and immediately call him to see his fives full.

Interested in comments on all streets.