I have just began gaming with my horse ( we usually do performance classes, english/ western pleasure/ equitation). He can trot and canter through every pattern perfectly ( keyhole, pole bending, figure 8, international flags, 2 barrel flag race, and texas barrels). The problem is, when I ask him to gallop, he just doesn't. Sometimes he just remains at the same pace, or bucks.
I have ran him before ( just around the arena and on trails and such) so I know he can gallop.
He is responsive to leg cues and has a relatively soft mouth.
What can I do to encourage him to gallop during gaming patterns?