My gelding rides and lunges good all except for his trot. He starts out at a slow steady speed (which I would prefer) but while were lunging or riding he will suddenly speed up in to a fast choppy trot. I have had my trainer watch me ride and she cant figure it out. She says you cant tell he is going to do it untill it happens and that I dont do anything to make him speed up. He does this with everyone who rides him. Any suggestions?