2001 Chevy Express 3500 RV (brake issue). New rotors, pads, shoes, one drum replaced, one machined, new rubber lines. Any ideas?

Likely air in the system.

First off keep the points, there useless anyway. If you don't believe me look at the top ten people on the right of the screen, they haven't changed in a year or so. In fact since your a long time user report my answer, it's the only time I get to email someone at this useless Yahoo site.

Okay that said. Your problem. Not much to go on other then you don't think the brakes are working properly. Have you driven a heavy vehicle before? I'm going to assume you have and that is the reason your here. I have had one of our drivers complain her truck was not stopping like it should. I inspected all parts of the system (air brakes) and could not put my finger on it. I only went to this terminal once a week to service them so I told her I would replace her almost new brake linings next week. My boss would have flipped out had he known anything to do with it. She told me it worked. I'm not sure that will work for you as you seem to have other work done. I also had my own business where I drove a 11,000 pound truck which I thought like you it didn't stop like it should. I put bigger wheel cylinders on the truck and it made no difference. I have studied the workings of the brake systems for air brake and hydraulic systems and one of the things I have learned is a simple thing. At lease in hydraulic systems you put the short shoe in front. What does that mean, if you look at the replacement shoes in the box there are two shoes that have less pad then the other two. If they are the first to make contact they will "pull" the other shoe into the drum, short shoe up front. And since we are talking about stopping that would mean when the wheel is turning in a forward motion. In my shop my lead mechanic with years of experience didn't know that, maybe your people don't either. I realize there are things I touched on that many don't understand and some that can't If they or you wish to talk about this more you need to click on my avatar to contact me. Like I said long ago, keep the points just turn me in.

well the only thing that you haven't changed is the master cylinder, you could be looking at that, or improper bleeding of the brake fluid, possibly also incorrect assembly of brake components.

Why did you have just 1 drum replaced? that can leave greater chance of poor balance in the rear brakes.

Also really cheap brake parts can brake very poorly compared to OE spec or upgraded brakes (the shop that I work at simply won't use the low quality parts for this reason)

You replaced a brake line...did you do a scan tool bleed procedure? I'm betting your have air in the ABS valves.

How much brake fluid do you have in there? It's probably that or the stock brakes on that car are just really bad.