I've always had a tiny difference in performance with my 5.0's. Nice thing about twins is the ability to compare and swap parts.
However, to eliminate non engine factors, I started with having the props tuned. Small differences in the props can equal a few hundred RPM difference.
Next was basic tune up items. Plugs, cap/rotor, fluid/filter changes (don't forget the small gas filter inside the carb inlet. Carefully set the timing to spec using the prescribed method to insure base mode is set on ignition module.
With all that done, RPM difference was brought within a few hundred. After reading the plugs, I found the stbd was running a bit leaner than the port. For giggles, I swapped the carbs and ran another test run.
Problem followed the carb!! Rebuilt both (just to be safe) and issue is now gone.
Note: Incorrect timing was the main culprit, gunked up carb was just the icing on the cake.