99-04 Front calipers hanging up

What's with these things, seems to be fairly common that they drag, won't release all the way, or just plain get stuck. There's several threads on here of people having the same issue. Is the piston coating failing causing the phenolic to swell, or something else?
I've got them on two of my cars, and noticed how they both drag on one, so checked the other car, and found one drags, the other I can spin the wheel and it rotates a couple more times before it stops. With a beam style torque wrench on a lug nut it takes 12-15 foot pounds of torque to turn the rotor. I pulled the caliper, and blew air into the banjo bolt fitting and only piston came out, the other is stuck. I can rotate it, but that's all, can't get it to move otherwise, except to compress it with a c-clamp. Looks like I'll be going back to the cast iron 94-98 calipers.