Overheating rear end

Still working on this, so bizarre to be having a difficult problem with such a simplistic system.
I have swapped drums from side to side, no change
Checked the drums, they are well within spec and do not appear warped.
Confirmed it is a brake issue, removed the rear brake hose and capped it off and drove around for a while, rear hubs stayed dead cold to the touch. Hooked the rears back up again, hot brakes returned.
Swapped out the shoes on the left side for some gently used ones of a different brand from another car, no change.
Brake adjustment is fine, ebrake is not too tight, in fact it's too loose, lol
I can spin the wheels freely, hit the brakes, release, and the wheels spin freely again, so they're not dragging.
Thanks for all of the suggestions guys, I think my next line of attack is to flush the system, put fresh fluid in, and give it a good bleeding again. Not really sure what to do beyond that.