1998 truck rear brakes keep dragging?

Uh, sticky brake cables? calipers dragging? parking brake not released? drum brake shoes worn into backing plates? Hardware fell apart inside drum? bent pedal pushrod. wrong fluid added to master cylinder? return springs weak and inadequate, overheated.

shoes over adjusted? lubricant or fluid leaked on shoe lining?

But you could always take it in for a free inspection and find out in 10 minutes to an hour depending how far they can tear down.