Change the brake hoses. Those can get soft with age and can suck together under hard braking and then the caliper will retain hydraulic pressure causing brake drag. When this happens, the caliper will still collapse normally when you pull them off. Also a good idea to change those anyway. I never trust those hoses after about 100k miles. I've had them bust before. They're fairly cheap to replace anyway.

Also, I'd reccommend adding anti-drag brake clips to the pads/calipers. They're not available at Auto Zone but you can get them from NAPA and also ROckAuto.com. They are about $5. They definitely seem to help.