You open a rear brake bleeder and fluid squirts out when you press on the pedal? I mention that though you say it was bled, if you used a bleeder of some type it won't show how things are operating. If you get a good fluid squirt, then it is probably the wheel brake cylinders. No squirt, then work your way backward trying to break apart each line connection and press the pedal at each to see if there is a clogged line all the way to the proportioning valve. Then the lines out of then into it. From a snow area, road salt will rust the outside to cause breaks. I have seen some as they passed through narrow passages have the rust expand internally and crush the rust thinned line in onto itself and totally stop it up.