[95 S_Trucker]

Fuel pressure should be 60-66(KOEO) for the OLD STYLE spider injector.

Fuel pressure should be 55-62(KOEO) for the NEW STYLE spider injector.

58 is within the spec for the new style injector, but check fuel pressure without the engine running.

An external coolant leak shouldn't cause a misfire.

Fuel pressure regulators do leak, but it will run bad all the time, be very hard to start(flooded), and cylinders 3 and 5 spark plugs will be black.

Pinching the return line will test for a weak pump. Its called a "dead head" test. It will not test the regulator. I don't think its necessary on your truck.

I don't think you have a fuel issue.

Most likely you have an ignition issue(distributor caps are very common), or sticking valve guides.(There is a TSB for misfire while towing on accelerating uphill)

Ask a mod to move this to the 88-98 section(since your truck is a GMT400), where it belongs.