just sounds as if the shoes are not adjusted right to be honest fella, you say you have adjusted the cable i take it you mean by the 2 plastic locking wheels?
have you adjusted the shoes themselves on the shoe adjuster inside the drum?just by using a screw driver lever it to spec so they just skim the inside of the drum
have had it before were the shoe lever that pivots has been seized could be that too, might just need freeing off
hope that helps