Equine Metabolic Syndrome?

I have a Quarab gelding of unknown age (estimated to be between 7 and 10). I have owned him for three years and every spring he contracts a mysterious offness in his gait. It is very subtle, and only detectable on the ground if you know what to look for. However, I am his only rider and am always able to pick up anything different in his movement. The first spring he abscessed, which was expected as his shoes were pulled just a few weeks earlier, but last year there was no apparent cause for it. He was lethargic and depressed, also. I was in contact with my vet and he was actually scheduled to do a lameness evaluation, but a few days before it was scheduled, my horse was acting miraculously better. This spring, he has the same symptoms. My trimmer has been recommending for months now to get him off of grain completely, however, he still gets a small amount against my will (long story). She also warns me now of laminitis. The pony he is with is potbellied and has cresty deposits on his neck and a swollen sheath, so I think he may have the same problem. My horse has a fatty sheath, and a very slightly crested neck. I have spent countless hours both last year and this year researching and asking different people regarding my horse's weird lameness and behavior, and I have not come to any sort of definitive conclusion until now. Do you agree that he might have EMS, along with the pony? If not, what else do you think it could be? Money is tight now, so unless there is a good chance there is actually something concerning about him, I'd rather not get the vet involved. If, however, you guys think he could benefit from getting some blood tests and examinations done, I will certainly do so.