Get in touch with Cliff Ruggles:

http://www.cliffshighperformance.com/

This guy is a Jedi Master with a GM four barrel. He can completely rebuild your unit, custom-tuning it to suit your specific application. Or he'll sell you parts (jets, metering rods, choke pull-offs, high-flow fuel inlets, etc.) so that you can tune it yourself.

He's a great guy and tremendous resource. The dude will actually take the time to talk with you on the phone about your carb problems.