I'd love to see some before pics and some after pics (in a couple of months). In the course of my internship I've been interviewing quite a few people about why they feed grain to their horses (very few people had actual reasons). Yesterday I met with my Equine Nutrition professor who is also the "go-to" person for hard equine nutrition problems (if she doesn't know she finds out) and I actually asked her what she recommends for hard keepers (specifically TBs). She told me the first thing they do is maximize the forage intake preferably so that they have forage in front of them all day and they make sure that the hay is of the best quality they can find. So good luck! Just remember to give it enough time
Oh yeah and I wouldn't worry about the protien thing. Good alfalfa has a protein level of like 20% or and good grass hay (not overly mature stemmy stuff) has a protien level around 18%. Pasture is at 26%, corn 9.4%, and oats are 13.6%. Your horse's protein needs can be met perfectly by hay, providing it is of good quality.