have you completely removed the caliper and cleaned where the mounting bracket slides?
there are the two rubber boots on the caliper where the bracket slides back and fourth.
they can get gummed up and need to be cleaned out and regrease them. also a little grease on the pins for the pads helps.
i had my rear caliper completely lock up due to those little slides. i had to let some penetrating lube soak in there overnight just to get mine to bust loose.
