Hello Matt
I had the same problem for a long time, no-one could solve the problem, freinds, brake shops, etc... I replaced all the brake lines in the frame last winter and comes to find out that I had a line pinched between the frame and the front crossmember, when the frame flexed it crushed the tube about 50%. It happened to me it could happen to you, who knows?
Just something to think about, Good luck.
Bill