Have you ever tried him on Happy Hoof or Dengie Healthy Hooves? Both do a molasses free version I'm sure. I think Zi was on that before he came to us. I reckon it could have something to do with his behaviour - sounds like it anyway. I know if Storm (of course she's not ridden now) eats too much Senior mix she can get very silly in hand - I give her a sprinkle (literally) of it to get her medication down mixed in with grass nuts.Went out this morning, very forward boy, so I knew what was coming. Long trot, then got off BEFORE the nonsense. Sure enough, he got silly. I think I may have had a lightbulb moment. I've upped his feed, because we're low on hay, and this may be the problem. He wants to GO! He's not arguing with me, apart from wanting to go forward - very forward! Got on again, still forward but manageable. When we got to the yard, I turned him away from home, and his argument was just not to go. No rearing or bucking, just stationary. He eventually walked on for me, so we ended on a good note. I'm going to the feed store today, and buying pure grass food. He usually gets a teeny handful of molli, but he's been getting more recently - I know - pure sugar!!! Cross your fingers that I'm right.
I find Allen and Page very good for not firing them up too - and you can feed quite a lot of that if you are short on hay.