Left rear outside brake pad is the only pad that wearing out.

NEW caliper AND bracket?

All calipers have got slide back and forth on the mounting bracket when bolted in place... That caliper is NOT doing this!!.... Remove bracket and repair 'frozen mounting slides'... or as stated replace it! .. Also, this will usually improve braking and have LESS pedal travel as well..

anytime you or anyone else,including myself replaces brake pads,you should always grease the slide pins in the caliper.im sure you have a caliper sticking.