Nervous and Fidgety Horses and Weight Issues - Is There A Link Here?

The last two TBs we got off the track included a mare and a gelding. The mare adjusted to life on our farm wonderfully, and after a brief period of weight issues and skin fungus, she is now totally "normal".
The gelding, who we now call "Monty", is a different matter. We have had him a year and a half and are still having weight issues with him.
I have tried everything the feed stores have to offer - high fat feeds, pelleted feeds, weight gain supplements, alfalfa pellets, alfalfa cubes, corn oil, yadda yadda yadda........ in addition to free choice quality hay and fresh water. And while we did see a lot of improvement (For a while last summer I thought he was just going to die; and no one could figure out what was wrong.) I still think he looks ribby and underweight.

This morning when I went to the barn to feed, I had a revelation, I think. I had turned Monty out in the barn yard to eat his nightly hay, as I think the mares in the herd paddock don't let him eat the hay we set out for all of them, and chase him off.

 There, in the barn yard spongy wet turf, he had worn a trench next to the fence from pacing it all.night.long. It looked like someone had gone in there with a shovel and dug out a shallow trench along the fence line! The 50 lb. chunk of hay I had set out for him last evening was gone, as well as several other leftover hay droppings under the hayloft door; so I know he ate.

 I then proceeded to feed him his morning ration (Several pounds of high fat sweet feed and "hay replacer" pellet - a new experiment) in his stall, and left the door open for him, while I fed the other horses and did morning chores. He would grab a bite from his feeder, and walk out, up the isle, make a large circle in the barnyard, and walk back - (rinse and repeat)......
I shut the stall door. He grabs a bite, circles his stall, and gets another.

About a month ago, we had to have his pasture buddy, a very aged QH gelding, put down. After that, we have been trying to gradually integrate him into the herd with the other 5 horses. And he has gotten increasingly fidgety, nervous, and worries all the time.

We only stall the horses for nasty weather, and feeding, and to hold the horses while we're doing various chores in the pastures and have to have the gates open for tractors, fence repairs, etc. And when he is in his stall, he paces, weaves, and works on shredding his heavy plastic feeder that is attached to the wall. He doesn't crib, just shreds.

So I am beginning to wonder now if his nervousness, worrying, and fidgeting is a factor in our on going weight gain issue. Has anyone else had a OTTB do this? Do calming supplements work? I've thought of giving those a try.

I also switched my radio station from hard rock to classical.

He just seems to be getting worse since he lost his buddy and cannot seem to get along with the other horses and just stands in the corner waiting for me to come and feed him twice a day; pacing and weaving.
I could understand it if I kept him in a stall 24/7 but I don't. It's like paranoid stall behavior in a paddock/pasture situation.

?????????? 

PS - He's not being ridden yet, because he was so "sick" last summer and fall and no one could figure out what was wrong so we didn't put him under any training stresses. Then in the fall he was plagued by abscesses in both front feet and was lame for a couple of months while we worked on it with our farrier. He walked around in  Easy Boots for weeks. Even at his hoof trimming appt. a couple of weeks ago, there were still issues from the abscesses. I have only just in the past few weeks started working him a little bit on a lounge line. So perhaps the nervousness is penned up energy finding a release. I dunno. I am stumped.

Sooooo....

I rode in my vintage jods yesterday and it was interesting. I didn't wear tall boots; I actually wore a new pair of  western Justin ropers I had bought recently because they need breaking-in.
Anyhoo, the jods were "tight" in some places and loose in others - obviously; they're loose through the hips.:P
I think it was less "tight" and more that they have no stretch and it is an unusual feeling, for someone used to riding in modern day stretchy breeches.
But for the most part I can report that these vintage jods are super comfy!