What might cause a low RPM misfire that goes away around 4000RPM in an racing big block chev have checked distrubtor battery compression carb leads?

I'm assuming that the engine you describe is somewhat high compression and as such both the sparkplugs and the plug wires need to be in better than average condition or you may experience some misfiring Also, if you have an exhaust gas analyzer available, check to see if your engine is running a little lean at lower speed. BTW, at 4000 RPM it's also possible that you just can't TELL that the engine is misfiring any more. My contribution: On racing big blocks with misfires, I try to reduce the plug gaps, say to .035 or less and then later open them up if the problem is corrected. Don't use projected nose spark plugs in a high compession engine. Use the standard nose plug, I like NGK these days. I hate .060 gaps in a racing engine. I assume you have a quality coil and a good MSD ignition box. Racing engines like a lot of initial advance or fixed advance with a locked out distributor. Check from distributor rotor alignment when at firing position. The MSD website has a tech page to show how. Another thought is that holley carbs can be very rich at idle and part power and cause a rich misfire. Correcting this is a whole other subject.