Gains Mod, or a multiplier on the amount of base powerlevel you gain per point of damage, can be affected by many things:
Race Gains: The inherent growth of your race.
EQ Gains: Increased by equipment, particularly rare or weighted items.
Double Gains: Earned through Quest Points; permanent effect.
RPP Gains: By role-playing and spending RPP, you may purchase boosts.
Global Gains: Increased by the amount of players online at once.
Double Exp: An Immortal gift that doubles pl gains. Do not request.
Enhanced Gains: A donation bonus that increases combat gains.