I've replaced front rotors, pads, and calipers about 2 years ago.

Quite recently, rear shoes were replaced (by a friend) and I started getting a vibration when braking. Suspecting warped drums, I replaced those last week...and still have the issue.

Issue:
When stopping from highway speeds, getting a pretty severe vibration that can shake the whole cab. The steering wheel doesn't shake; it "feels like" it's in the rear.
I vice-gripped the brake line leading to the rear to temporarily disable it while testing, and it didn't vibrate (I know, kinda harsh, but I was frustrated).
Testing by using the e-brake though yielded no vibration (I later found only the passenger-side was engaging w/ the e-brake).
Inspecting the rear brake hardware showed that the adjusting-thingy (that adjusts the shoes when the e-brake is engaged) was rusted locked...so they're definitely not adjusted properly, and the drivers-side e-brake mechanism wasn't even budging.

My next step seems to be replacing the ebrake and adjuster-thingy...but thought I'd check here to see if there may be other opinions/leads?

Thanks for any advice!
Mark