Parking brake driving me nuts!

[AirSpeed]

I can't get the parking brake to hold my truck on even the slightest incline. My brakes and all the components are in great condition, I adjusted them so they slightly drag, I adjusted the parking brake pedal so its solid at about 1/3rd the way down and they still won't hold. Everything behind the drum operates smoothly. I lubed the park brake cable and it all operates as it should but it still won't hold my truck even on flat ground. I have worked on plenty of brakes but this has me pulling my face off! Any ideas?
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