If you pulled the drum and there was oil/grease on the magnet and drum, then it was on the shoes as well. If oil/grease gets on the shoes, they are junk and Brake Cleaner will not get it off. Take the drums to your local guy and have them turned to get the glazing off them and replace the shoes and seals. Repack the bearings and you'll be good to go.
If I had to guess...I would say you have easy lube axles with the grease fitting on the hub. I personally have never had any luck with them, others have. You may get Lippert to do something for you under warranty.
And yes you should have full braking power weather you are towing with a 1/2ton or a dually.
