I only use sealant around the water passages, most newer gaskets are silicone coated and any extra sealer can make them 'move".
Another possibility is any machine work done on the block or heads could be making them not align as they are supposed to.
Agreed. You might want to run a machinists straight edge over the machined surfaces and make sure they are within tolerance.
Does't EDELBROCK have their own brand of gaskets? (I always use FEL-PRO)