Drum brake thumping

[salmonz]

So I changed the rear shoes in my 07 Yaris Sedan with aftermarket shoes and new spring hardware but kept the original factory drums on, bled the brakes, now I'm having a thumping noise when applying the brake at 40km/hr or less. I feel it through the pedal but it's definitely coming from the rear.

Here's what I've done to try to fix the problem but didn't work:
1. Stretched the hold down springs to put more pressure on the shoes.
2. Made sure the self adjuster was sitting correctly.
3. Made sure the shoes and the drum were snug enough that there isn't any major gaps between the drums and shoes.
4. Lubed the adjuster, lubed contact points on backing plate.
5. Checked for wheel bearing play - none.
6. Checked for debris, i.e. rocks - none.
7. Checked all springs for tension and that everything was sitting properly.
8. Checked wheel cylinder for leaks - none.

What I'm thinking of doing (in order):
1. Replacing hardware with factory hardware.
2. Replacing drums.

What may be causing this and how do I fix it?