Did he colic with his prior owner? What is your boarding situation like? My anecdote:
My TB mare colicked the day I bought her in 2021 as a 4yo and proceeded to colic more than 20 times over the course of the next year and a half - including 3 hospitalizations, often happening bi-weekly, etc. Gas, impaction, spasmodic, you name it, she’s had it. Many displacements. Luckily no surgery, but since I was at the barn all day every day I caught every single one quickly and had the vet on the way.
We did ALL the tests with no resolution and after her 2nd and 3rd hospital visits the local hospital urged me to put her on the pellet-only diet, but I ultimately decided not to move forward with it due to her high anxiety/stress mentality, ulcer history, boarding restrictions, the fact that she is an extremely hard keeper, and my desire to try to try to get her into a situation with turnout. Though I pocketed it as something to consider in the future.
I instead did the opposite - working with my primary vet I moved her to 24/7 all-you-can-eat hay access, tested the hay to make sure it was high quality, and also added Assure Guard Gold to her diet while pulling her completely off of all grain (she cannot even have a handful of a ration balancer, she is that sensitive). I instead moved her to soaked beet pulp 2x/day with minimal supplements. That made a HUGE difference initially, drastically reducing her colic frequency and severity and then a few months later I finally moved her to a quieter barn that could continue the 24/7 hay access while also giving her 8-10 hours a day of grass turnout in a 10 acre field with friends (prior barn she was lucky to get 45 mins/day on small dry lot with one other horse). This made the biggest difference for her, mentally/emotionally as well as physically. She now * knock on wood * only colics approx 1x/year very mild, and after employing the expertise of a nutritionist to advise on the forage-only diet she has put SO much weight on that people don’t believe me when I say she doesn’t get grain. She is now 7yo, in full work and jumping 1.0-1.05m.
I’m not sure what your barn and feeding situation is like, but if possible I would highly recommend trying a quieter living situation with constant hay access/ample turnout and moving forage-only. Even if only temporarily to see if it makes a difference. I loved the barn we were at and it was very hard for me to leave - but personally, I prefer to try the simplest route first before diving into different tests/medicinal routes or exploratory surgery which was next on our list. I’ve found that often the hospitals like to try to hyper-focus on little things rather than look at the big picture first