I don’t want to rain on your parade, but I went through a deterioration with my early retiree starting at about 5 and culminating somewhere around 7. My suspicion was somewhere in the neck, although he did constantly present as backsore. But the fact that even a surcingle caused him to be girthy and reactive made me feel there was more than just the back going on (this was before kissing spine sx). We threw everything at him in a last ditch attempt, osphos, mesotherapy, neck injections and back injections over the course of 10 days. And for 4 months he was amazing. I was shocked at how much the suspension in his trot had slowly deteriorated without me noticing it, because even without the suspension he was a hack winner.
And then just like that it wore off, and he was worse than before. I gave him a couple months off to see if that would change anything and the last two times I worked him were disastrous. Day one was me lunging him with the tack on. He took about 8,000 steps to go 50 yd to get to the arena and then just did that horrible girthy walk trot and canter. He finally loosened up a little bit when he was cantering to the right and then he heard a noise in the woods and lifted his head. Not in spook or alarm but just general interest, and went from zero to bronc in one step. I truly believe that it was like an electric shock, and that was the moment I realized that this horse had no intention or control over when he would bronc, and he would kill me one day. The next day I took him out and just tacked him up in the arena just to finish on a different/good note. As soon as I slightly tightened the girth he buckled down and then reared up and buckled and reared a couple times, and then fell over. I made him get up so I could safely remove the tack and that was both the first time he did that in his entire life, and the last time he’s had tack on him!
But, to put a happy end on the story, if that hadn’t happened, I’d probably still be slogging along in the hunters and instead I pivoted and moved to combined driving and I’ve never enjoyed myself so much as when I made that change. So I like to think that these things happen for a reason