The E brake is also self adjusting (in the calipers) and works all the time every time, just as well down hill as up. Drum brakes are "self energising" in one direction only and tend to slip more backwards.
Most folks have found disk brake parking brakes to be problematic, which is why many manufacturers that use rear disks have a smaller drum brake that is mounted inside the disk hub. Many manufacturers are going back to rear drums because of the parking brake problem.
Also, drums are self energizing due to the rotation of the drum against the shoe. The friction of the drum on the shoe will pull the shoe into the drum (self energizing it), hence the need for all those return springs. One shoe is self energizing in one direction, the other is self energizing in the other direction. There is no difference between forward and backward.
As far as I know, you only have three choices for discs and parking brake, unless you want to fab your own.
The Front Range Off Road kit, using calipers with built in parking brake.
The Chevy rotors with Cadillac calipers: You'll have to have the hole in Chevy rotors opened up to fit on your hubs, and then make some kind of parking brake cable arrangement, and get metric-SAE hoses.
The Chevy rotors with T-case brake: Same trouble as above, except more expensive. The T-case parking brake has a significant mechanical advantage, since it gets the benefit of the axle ratio to stop the wheels.
At any rate, good luck with your problem. Let us know your solution.
