antifreeze disappears and motor misses. What could be wrong?

You either have a cracked block cylinder wall waterjacket/passage, a blown head gasket, or a cracked cylinder head water jacket/passage, leaking antifreeze into the combustion chambers(s). If the mileage is low then its worth paying to have it repaired but call around and ask for a rough estimate from a few garages in your area. If you can do the work yourself then start with an inspection camera in place of each spark plug and look for antifreeze in the combustion chamber. The labour costs to change a head gasket are high,almost the same as replacing the engine, but weiyth no guarantee at all. If the block is cracked then there's other damage to the engine, maybe antifreeze in with the oil as well, damaged pistons, broken piston rings, or damaged cylinder heads. A head gasket might be cheap, $30-80, but the labor involved is really high. Sometimes even the cylinder head(s) has/have to be reworked at a machine shop, adding to the repair costs.

That was my intake manifold. The 3.8 is notorious for the intakes going bad and leaking. $350 for the whole job with my mechanic.

Hi. You did pretty good then buddy. All the best to you.

It turned out to be the intake manifold.

Hi. So it looks like you're another one with the intake manifold being the cause. There must be some kind of defect in a batch of them at the factory. At least it's not a cracked block or head. All the best to you.