Thanks for posting the info on your grain.
Having one seriously metabolic horse and one trying to head that way (serious hoof issues go along with that), my opinion is to lose that grain and find something without the oats & corn and especially without the molasses :)
I'll bet if you ask them for the NSC (non-structural carbohydrate) percentage, it will be thru the roof and totally unacceptable.
While much more $$ than what you are paying, there are feeds out there that are much healthier for the horse's entire system, both metabolically and structurally. And I have found I don't need to feed nearly as much of better quality feeds, so the money issues are almost a wash.
If you don't have too many options, at the very least I would consider switching to a pelleted & stabilized rice bran, and add a pelleted vitamin/mineral supplement to it.
Rice bran is 20% fat but it is healthy fat. My metabolic horse went from being an air fern to having difficulty holding his weight. He is out on pasture 12-14 hours/day, gets one flake of hay when he comes in at night and was only getting 8 ounces of pelleted rice bran 2X/day to maintain a good weight.
I say WAS because I can't get Equi-Jewel rice bran anymore, so had to switch him to Purina's new WellSolve L/S feed. So far so good.
Having spent this past year learning how bad a high NSC percent is in horse feeds, I tend to get preachy about "losing it".
I also raised a son who was "food sensitive" and tried to keep him on the Feingold diet in his youth. Until I learned he traded his banana in for a Ho-Ho on the school bus one day --- then I had to set his 10 year old bad self down and give him a serious talk
I don't mean to offend anyone and apologize if I have. Maybe others will have a better idea :)