Get feet checked. My guy was going good late last summer and went footy but it looked more like bad behavior, till I noticed he walked a lot better on grassy, then acted really stupid just before gravel or rock (this was a horse used to doing rocky trails everyday).  Turned out the pasture chemistry had changed due to recent rain, so putting him on just hay started an improvement with 48 hours, plus visit from hoof trimmer. If this horse is new to barn, maybe a change in the hay or feed affected him.

 Lately my guy went from good to naughty as a huge new crop of mosquitos took off. Normal bug spray wasn't cutting it and he had a melt down during the ride due to mosquitos. I can't remember a recent year when they were this bad all of a sudden.

I would get someone qualified (a good chiropractor?) to check his back.  This horse may have strained something in his shoulder/back during the trailer ride to your stable (a sudden turn, a sudden stop, or maybe his neighbor got suddenly nasty and he tried to move away fast?)

  Since he has always been cold-backed I suspect that there was always something wrong and that the horse was just putting up with the pain, but with a fresh injury the horse may be trying to protect himself from further pain.  At least this is what I am "hearing" from your description.

Hey Barb,

My suggestion would be ulcers as well, he could be upset from the move to the new barn.