When it affects all 4 calipers like that, I wonder it there is an issue with the master cylinder not returning properly. You could jack up all 4 wheels, either all at the same time or one at a time, have an assistant apply the brake pedal and release it, while you spin the wheel and see if the caliper released immediately or seriously drags (or stays locked-up). Then see if it affects just one or two calipers, or all four. Also, does cracking open the bleeder valve allow the caliper to release? If so, then you have an issue up stream and not with the caliper itself.
|