Ridecamp: [RC] [RC] [Guest] Help with pinto/arab - trouble going down hills and more.....advice

I've known two horses who exhibited this very same problem.  Whether the reasons are the same for your horse are to be determined, of course, but both of the horses I observed simply needed to learn to go down hill.
As you may imagine, it apparently takes a lot of grace and coordination to keep track of four legs as the relatively uninitiated stumbles down a hill.
One of the horses I mentioned was a gorgeous 17+ hand thoroughbred who had just arrived from England.  He was 6 years old at the time and watching this huge, otherwise graceful animal from the rear as he tried to move down a hill of even the mildest grade was positively scary.  
He displayed all the characteristics you mention.  I thought for sure there was something wrong with him.  That he may have even had some kind of neurological problem that only occured on downhills(?)---but that's how bad it was.  
The new owner (who was over 80 years old at the time) said he had seen this before and said the horse simply didn't know how to control his large, ungainly self in such circumstances.  Something horses usually learn when they're very young and much more flexible and resilient. 
He was, after all, absolutely sound and healthy in every other circumstance EXCEPT going down hills.
So in order to address the problem the owner would have the horse led down hills VERY VERY VERY slowly and gently on a lead rope. No rider. These were very mildly graded hills to begin with.  In fact, hardly any grade at all.  
First the horse, named Bally Bay,  would refuse emphatically to go down, including bucking...something this gentle gelding would never normally do.  
Once he started, he looked almost like he had a palsy.  The human holding him would have to be very careful to stay out of his way as the poor, very frightened, ver large guy would slowly and painstakingly make his way down the hill, sometimes at a slant as you mentioned, with his back legs crossing over each other and tripping him up and otherwise just step by step stumbling his way down.  This training went on for a while but the trick was to take him down a hill every day, getting progressively steeper only as his ability and confidence improved.  This way he didn't have time to forget and get frightened all over again.  I'm sorry to say I don't know how long it took, but Bally got steadily better and now he's a champ on the trail.  I don't remember it taking very long at all.  The training was consistent, though.

With the 2nd horse the problem was the exact same thing and handled the exact same way.  He came from Texas where there were no hills at all and found himself in the Santa Monica Mts.

'Hellooo!  What the hay are those huge durn things...."
"Why, they be mountains, son, and we be goin' down 'em!!!"
'Oh yeah???   Make me!'
"Ok."
And down they went.   :-)

Kathy