As far as keeping the tempo, do you mean you bump with hitch ever calf corresponds to whichever leg you are controlling at the time?
When left hit comes forward bump with left calf, and vice versa. As they start to "get" the tempo I skip the every stride bump, unless of course they want to stick - then you have to pay attention to every stride and try to feel when they shift weight with the hip but do NOT lift the leg (i.e. they stick) - that's when you'll need to use spur and catch it.
Perhaps try a little leg yield and some shoulder fore/shoulder-in with him. Turn on the haunches and turn on the forehand (especially the latter). Trot down the long side, turn on the forehand, trot down the long side, turn on the forehand. Trot down the long side, walk, then trot off. Change it up, make him have to use his legs in order to keep his balance. These are great exercises to mobilize and strengthen the hind end (especially shoulder-fore/shoulder-in, the "mother of all exercises"). Gradually introduce them with the help of your trainer and use them as excercises, not drills. long series of ground poles also help alot of horses, as well as cavaletti. It sounds like your horse has excellent health care from a number of angles.
I'm not too concerned about the uneven hips, as I know a horse with very uneven hips due to a foaling incident who has won through second level at recognized dressage shows (and is moving up still). No judge has ever commented.
So wanted to give you all an update on Sir - he is doing very well and executed his first complete and amazing flying change yesterday! His hind leg action is peppier than ever and his diagnosis is truly laziness. Once he understands that you mean for him to actually work he pops those suckers and looks great.
And a big thank you to everyone, especially Valentina - the key was buying a pair of longer spurs so that I could "catch" him without moving my entire leg backwards and confusing him. He is a solid 16'3" (looks 17) and I am a petite 5'4" - having the extra spur length allows me to give him gentle aids and now I can move his hind end with just a slight tap. I used to have to twist my body to move my leg far enough back with enough strength behind it to press his hind end over. Now that I have the control over his hind end and ease of straightening his body, I can more easily create the impulsion and "pep."
So great to read all of this! Not to hijack , but reading the original post, I felt like I was the one writing it! My 4 year old WB drags his right hind toe at the trot (not at the walk or the canter, and only when he's going right). He's been checked out by a vet and declared sound so my trainer and I both think it's just laziness. With timed tapping of the dressage whip on that side (or if he's in a spookier mood ) he picks it up just fine and loves caveletti (sp?) and never hits it.. But it's great to hear that many young horses have the same issue and get better. (He also has a LOT of growing yet to do as he was in his gawky, looks-like-a-2-yo-not-a-4-yo stage until a couple weeks ago.) Also I've been doing a stretch that the chiro showed me where you cup your hand over the point of the hip and drag it down, applying slight pressure (you do this on the opposite side of the dragging toe) and it seems to have helped quite a bit (I do it 3-4 times before every ride). (hope that makes sense!)