I rewrote the whole plugin from scratch and added a feature for customizing a player's max levels based on permissions. Everything is now much cleaner and I will be able to more easily add new features in the future. Since this is a complete makeover of the plugin, there might be issues. Please report any issues in the discussion section.

New Features:
Rank-Level-Booster: boost a players max level and combining level using permissions.

Players who wish to use the new features should reset their old configs!