Problem with Holley 4 bbl

Got a problem with my 750CFM VS on my 360.

It doesn't respond at all to idle mixture adjustments. The usually means that excess gas is entering the system. So I went through the usual suspects -

1) Float level too high - checked and was correct just barely trickling out of the hole.
2) Primary throttle blades opened too far - pulled the carb to check and was correct (transfer slot looked like a square).
3) Blown power valve - checked with tester and was not blown.
4) Fuel pressure too high - gauge shows 5.5 lbs pressure.

What have I overlooked?

It's frustrating and can't seem to find the problem other than something wrong with the carb that is leaking gas into the manifold. Plugs are gas fouled and I've went through 2 sets of new plugs and don't want to buy a 3rd until I find the problem. Gaskets seem perfect.

Thanks.