Gaited Horse Trainer, Larry Whitesell...
Demonstrates a great exercise you can do with your horse to help get rid of the pace and learn to gait properly.
As with any training
It takes time for the horse to develop the proper muscles to perform the movement you're asking him or her to complete. So you will need to work on this exercise frequently and for a period of time to see improvement.
Reference:
Larry Whitesell Gaited Horsemanship, https://www.facebook.com/370199186849/videos/vb.370199186849/10153814447881850/?type=2&theater, Retrieved Nov 5, 2017