Rear Brake Drums

Need some advice. I have replaced the rear brakes in total inc Drums on a K12 I now have a knock under med to heavy braking I have re checked and can see nothing Obvious. If you brake progressively its fine. HELP!!!
I assume the rear brakes totally shot, "a picture of the open drums would be beneficial to the forum" I would also check the rear dampers, as these tend to thump when braking if they are worn out?:unsure:
Hi. Just a thought....I know on some cars it is possible to get the shoes mixed up . Did you fit the leading edge the correct way for the side of vehicle.? When you look at shoes fitted to back plate the linings on each of the shoes should look like they're being pushed off in the direction of rotation . Just a thought. Good luck.