15/16th mc resolved my front disc, rear drum, manual brakes on E Body. Had same issue as you describe when running 1 1/8th mc. Found Dorman 4 bolt mc 15/16 on Amazon for less than 50 bucks that did the job. Also able to switch from really filthy dirty pads which were soft and did help braking some with 1 1/8 to very clean ceramic pads after switch to 15/16th pads.
