could the intake be holding my low end down?

Exactly.the number 1 reason why guys lose bottom end power with a single plane is the carb is too big. You can usually tune around it, but most guys don't. A dual plane intake will take a bigger carb.

Done correctly, and DP intake loses every time. In both power, driveablity and fuel mileage.
Question sir.:
Steve Dulcich says that too big of a carburetor is not a problem with the Edelbrock carb, utilizing an 800cfm on a 318 after blowing up his 408 in his truck.

Is that negated because he used his rpm airgap dual plane?