There are a few things you might want to check in the rear. Rapid pad wear could be caused by a sticking caliper/piston, residual pressure in the line, or parking brake adjustment. I agree with the earlier post that checking the parking break adjustment would be tops since the caliper had been replaced.
If the parking brake is not the issue, then there is an easy test to see if it is a mechanical or hydraulic issue creating the drag.
When you get the brake to drag get the rear off the ground. Rotate the wheel to feel the resistance. Then, while rotating the wheel loosen the bleeder screw. If the caliper releases then there is residual pressure in the line. You need to then find the restriction which will most likely be a line or hose associated with that caliper since the other one is not dragging.
If the caliper does not release then it is a mechanical drag. This can be caused by sliders or pins, stuck piston, or pads that are bound up in the caliper.
The uneven pad wear on the other caliper is an alignment issue. Be sure there is no buildup in the caliper where the pads slide. If it restricts pad movement upon return it will cause the pads to **** and an uneven wear will result. Make sure the pad slides/abutments are clean and lubed both under and on top of the abutment anti-rattle clip, Be sure to use a high-temp synthetic brake lubricant when doing service on the brakes.
Hope the info helps a little.