I replaced my MC and booster with the upgraded set I've read about from a 95 model XJ.
Everything bolted up nicely. Kept the original proportioning valve though.
Replaced the front rotors, pads AND calipers (after breaking off the bleed screws!), front hoses with stainless lines.

When road testing I've noticed when accelerating from stop, it's like I'm dragging a bridge behind me. Very tough on the engine and no zip.
However the brakes work 200% better than they ever have.
I can push and pull the vehicle by hand in the garage no problem with no brake dragging.
Now I have not tried this with the engine running.

Any thoughts?
Could the forward motion of the rear axle be binding up my rear drums?
Could the brake pedal be pushing the booster in just a bit causing all brakes to bind?
Could there be something wrong with the booster causing braking?

 

Could the brake pedal be pushing the booster in just a bit causing all brakes to bind?
yes. Read the seizing front wheels thread re push rod adjustment a couple threads down the page.

( If you replaced the mc this is definitely a possibility)