Have you adj. the rear shoe's? clearance is critical on rear drum and front disc
combinations. Too much clearance between the rear shoes and the drum will make the front disc's work harder with less stopping power. That might be your problem as if you need to use both feet on the brake peddle to stop.
You can check your power brake booster by starting your engine and shutting it off then pop the vacuum fitting off the booster. If it doesn't have a wooshing sound, your loosing brake assist from the booster because of a bad diaphragm causing a vacuum leak. This will also cause erratic idle problems but will still run smooth going down the road.