Rear Hazards not working

I presume you have tired replacing the bulbs. If not I'd do that.

Investigate the bimetalic strip(s) that ticks the hazard lights for corrosion or other damages.

Check the wiring harness that runs under the bed for damage.

Ensure your battery ground makes a soild connection.

I'd also clean and sand the blub sockets to ensure a soild connection.

I'd give the fuse box pcb a look I've seen many terribly water damaged and corroded chevy and gm fuse box pcbs.

I'd also test the voltage across of the light socket between your body and the hot wire

And compare it the voltage potential across the two pins of the light socket.

A bad grounding to the frame, fuse or blub is typically the cause for lighting related issues.