In the skill description for acrobatics in the section about moving through threatened squares, it states that there are abilities that allow you to move through at full speed:
Move Through Threatened Squares
In addition, you can move through a threatened square without provoking an attack of opportunity from an enemy by using Acrobatics. When moving in this way, you move at half speed. You can move at full speed by increasing the DC of the check by 10. You cannot use Acrobatics to move past foes if your speed is reduced due to carrying a medium or heavy load or wearing medium or heavy armor. If an ability allows you to move at full speed under such conditions, you can use Acrobatics to move past foes. You can use Acrobatics in this way while prone, but doing so requires a full-round action to move 5 feet, and the DC is increased by 5. If you attempt to move through an enemy’s space and fail the check, you lose the move action and provoke an attack of opportunity.
What are the abilities it's talking about? Is there a feat a gunslinger could take to get this ability?