I bought my horse from the Amish, as a cart and riding horse. He did not have much training under saddle. But when you were driving him he only had one speed, fast uncollected trot, as soon as he felt weight in the cart he was 100 yards down the road before I sat down. The first 2 months all we did was walk slow and stop, sometimes we I just got in the cart and had someone head him for 5-15 min then unharnessed. As soon as he got to fast we would stop and stand for a while. Alot of the time it was walk 20 steps stand for 3 min, walk 10 steps stand a min. I still, 7 years later have him stand at least a min
after I get in the cart, before I ask him to walk on.
Same with the trot, he had no idea that there were different speeds that he could go. As soon as he got fast at the trot I would either stop, bend or circle. A John Lyons instructor that was giving me a hand also suggested speeding him up then slowing him back down, asking for variations in speed, getting him used to the differences. Now he loves trotting slow, sometimes he trots so slow I think he is going to fall over.
Good luck, Photos please.