I know nothing about AQHA nor about western but I do know English pretty well.
So I'm going to give you a check list for English.
He needs to be much more forward moving especially in that hind.. those hind legs need to reach underneath him. Reins should be shorter so you are connected and he can feel your seat and rein half halts. Depending on the style, your seat and stirrup length will vary. I'm starting Dressage so I deal more with deep seat riding and longer stirrups.
Incorporating half halts would re-balance him and start getting him more on his hind end when paired with transitions, figures (figure eights, circles, serpentines, spiraling in and then out, etc.)
He looks like a fun ride :) Best of luck in your classes!
"Strength is the ability to use a muscle without tension"