Doesn't sound as though you're fronts are doing much and they typically doe 80% or so of the braking.
I'll repeat one more time PRESSURE TEST 1st. at the master preferably, Dual master? buy two gauges, you'll need them at the wheels as well 2nd. At the front 3rd. At the rear The numbers will confirm or eliminate the hydraulics, air, leverage ratios etc. Not trying to be a jerk but,
