Hello with respect you are doing a lot of seat driving and this has put you sitting on the back of your bottom and it has tipped your pelvic so that your seat is behind your whole lower leg this can have a slowing down affect on your horse as it feels like you are behind his movement.

He is not tracking up and he is pulling him self along with his front end, he loses his balance from time to time.

It just may be worth having his pelvic looked at as he appears unable to come through and he is a little weak through his back end.

There is a test you can do pop a bridle on him and ask him to turn tightly to the inside to do a full turn
holding him from the ground when ask to turn he should cross the leg on the inside over the front of the outside leg to make the turn if he can not cross the inside leg over but pivots on the inside leg to turn he may have back/pelvic problem try this both sides.