I remember how hard i had to turn the tool the first time i did my rear brakes, though.....
I only found out the last time i did my rear brakes, when using the caliper winding tool, as you turn the handle you may only get one turn on it or less then you have to loosen the hex part off with a spanner, then turn the handle, then loosen it off with a spanner, then turn the handle.......and so on, otherwise it locks up tight and the piston does'nt want to go it.
Dunno if that would
help, you might not have needed new calipers.