I have a 1993 gmc suburban that has a code 54. I just stopped running at about 70 mph and wouldnt start back. It is said that the wiring harness could be bad and not the fuel pump is this true.
I doubt it. I’d say you have a short somewhere that shut the fuel injectors off. My advice would be to check for blown fuses first. When you find it, you’ll have to find the short, and that may be a bit of an adventure. My older F250 did a similar thing when the fuel bowl heater shorted out. We went through several fuses, going larger in amperage till finally we just shorted the thing with a couple screw drivers long enough to find the smoke.
I am familiar with Ford and not GMC. The Ford also senses the impact switch in series being open. I would be looking at where that switch is in the circuit. These switches can become flaky and need to be reset. The location also makes them prone to electrical connector problems.
The GMC Suburban doesn’t use a inertia/impact switch.