Metro Power Loss

1995 Geo Metro. 133 thousand miles. Loud rattle from engine, massive loss of power at lower RPM, low vacuum pressure, not blown head gasket (ruled that out), going to replace all vacuum hoses, advanced vacuum switch under distributor, and bypass catalytic converter, any other options I'm missing?

might be a burned valve, check compression

With a rattle from the engine, it's almost certainly going to need a rebuild. Probably a broken piston, they're pretty common. At 133K miles it's getting close to where you'd expect it anyway.

As suggested get a compression gauge. Engine warm, all plugs out, wide open throttle. 200 psi factory, 150 psi minimum.