Help needed with a 'hot' horse

I have a 10y/o AQHA named Nico. I have disected every which reason why he could be hot and came down to feed. We feed 12% sweet feed at the barn. I've heard that this can be the worst thing to feed an 'energetic' horse. I am willing and able to switch but was wondering if anyone had any suggestions on what to start with? I heard that low carb feeds are best for horses with 'hot' tendancies. When I was 18, I would have loved this horse for all his energy...at 30, not so much.
I checked these possible causes off the list...
Maybe I developed into a 'heavy handed rider'...nope. He reacts the same on a tight rein as he does a loose one. He pushes past the bit or hack and does the 'ants in the pants dance' almost constantly.
Maybe I don't ride enough. Nope. I ride 3 days a week and he is just as hot when he leaves the barn as when he comes back.
Maybe he is in pain? Nope. I am a massage therapist and if there was a knot on this horses body, I would know about it.
Maybe he is bored? This one is still up for consideration. We ring ride before shows but once he gets bored, he does get a little more pushy. On trails, the other horses have to trot to keep up with his walk (an it ain't because he's leggy...hes only 14.2)
Maybe all I do is canter and run and that's what he wants? This one is a sure-fire NO. I've spent months only allowing him to walk and trot. He is actually hot at the walk.
Maybe he has ill fitting tack? I don't think so. The western saddle that I ride is a big horn and it fits him like it was made for him. I've been through 2 dozen (no joke) bits to find what he likes best. In the ring I can ride him with a loose ring snaffle as im not afraid of him running off with me in the arena. On trail, he rides a copper mouthed wonder bit. Though he doesn't like this one as much, when he gets a bit much, this is the only bit that can stop him.
Please help if you can...I love his personality, his demeanor, his big fat butt, but this GO GO GO! Thing is getting old.

3 days a week - doing what? How hard are the workouts? I work my "A" horse 5 days a week and he works but is not in the least tired when I am done.

His pain could be skeletal - out of alignment - or in the deep tissue and you would not find it.

I would think if it was a sugar buzz from his sweet feed that it would wear off like it does with people. So he would either be a spaz or dead and you say he is busy the whole time.

It sounds like you truly do not like his personality anymore. Maybe I am not understanding what you posted well enough but it sounds like this is how he has always been and you are not liking it now that you are getting a little more aware of it hurting when things go wrong.

We ride 3 days a week...we usually warm up with 20 minutes in the round pen and then 20-30 in the ring then 1.5hr trail ride. Its a moderatly challenging trail with lots of hills. As far as the pain being skeletal...he doesnt really carry any 'painful expression' and is generally a really happy guy. He's not that drawn faced bit in the teeth kinda guy...I like to think of him as the 'jack russel terrier' of horses. Since I bought him, this has gotten worse. I thought maybe it was just being ridden again (he sat for a year) but its worse now than our first ride. I really do think its the grains. He was never grained before he came to us. Thank you for your input. Ill keep all you said in mind.

Cut out his grain?

He could simply be a very stoic horse. There are standard signs for problems, but not all horses read the book.

I wish I could cut out his grains. I just think that he would probably be pretty angry if all his buddies were eating and he had to stand there empty handed. We've got it cut back a good bit. He does work a good bit and im afraid of him thinning down...Im just at a loss. In every other aspect of our relationship, he is perfect for me. And even when im riding him, I still love riding him. I've tried working on slowing him down...which he can do but resents it.

I can totally understand that from most other horses..he is very expressive and has no problem telling you when something hurts. Also, in my experience when there is skeletal, you will also find muscular. The only place he gets knots is in the upper hip area...probably from me holding him back so much.

Ding ding ding! We have a winner.

Horse goes fast, owner tries to slow him down, horse gets annoyed.

Lather rinse repeat.

Which leads to horse starting out stressed because they know riding will be stressful because owner will be trying to shove a round peg in a square hole the entire time so more stressed horse is more up.

Lather rinse repeat even more and things just keep getting worse and worse and worse.

So your solution is to just let him take off and run around like a maniac?