Loud knocking coming from engine

[TooMuchRock]

We just replaced a ton of things on the 2000 2.2 automatic cavalier. Waterpump, both 02 sensors, spark plugs, wires, changed the oil, remachine the head, changed the head gasket, serviced the transmission, and a few other things.
Now we have a problem. Recently the car has been shifting a little late from 3rd to 4th. Today we drove it to the store and it it reved up very loud, would not shift at all, and is making a really loud clunking/knocking/rattling noise coming from the engine.

What is wrong with this thing?

[shakewell]

You sure the sound isn't from the trans?

[TooMuchRock]

it does it when reving even if the car isn't moving.
It overheated in july i think, and we had everything redone, except well that.
Uncle says he thinks it could be the oil pump or torque converter.

[shakewell]

It's really hard to say, but it can still be the trans even if it's not in gear.