My horse? It was not low grade, he was pretty lame at onset (2-3/5?) though not drastic (no "founder stance" or anything, willing to move, but he was also on soft sand, painful to watch on gravel :/). Both vet and farrier confirmed laminitis and vet determined it was due to Cushings (which was simply confirmation of my thoughts). Xrays were clear. He came up lame my mother called me and I said to call the vet, it was not an ongoing thing. Now he hasn't been 100% since then but I suspect it will always be an ongoing thing at this point due to the Cushings/IR, but vet has cleared him since the initial episodes and his issues are managed (may be a mental block too, expecting pain, at times).
My suggestion is to take the horse where the ground is hard and have them move, walk, trot, and tight turns.
A hint with my gelding (MFT) is that he was always more of a trotter but since the initial episodes he tends to be more of a pacer. Interesting. I would look for slight differences in the gait since the norm.
The Cushings/IR diagnosis didn't surprise me as he was hugely obese when he came and has that classic look. He was 19 when diagnosed, and that summer hadn't quite shed out (bear in the winter but VERY sleek in the summer, he shed out to a summer coat that year but it was still .5-1" long, not normal).
Definitely where my brain goes for bilateral lameness!
It's really all about management and there is NO harm (and only benefit) to managing a horse like they are IR/Cushings. It's like some people may NEED to eat very healthy, lots of salads, etc, but it's not going to hurt anyone who doesn't need it to do that! A horse may just need shoes or whatever too, but I would expect that to be an ongoing thing, not a horse fine on pavement then sore on sand!
At his worst my gelding still walked pretty normally in a straight line on soft sand.