Measured WHERE? At the relay? The only place that matters is as close to the pump as you have access to the wire harness.
In general, GM uses under-sized wiring for the fuel pump. Often, more than two volts of voltage drop when the pump is running--about a volt-and-a-half on the supply wire, and another volt on the ground wire, at least that's what I've measured on a couple of Luminas. Industry standards would be for 12-gauge wire given the length and the amperage draw. I think GM used 16-gauge.
The best way to diagnose electrical problems with these fuel pumps is with a low-amperage probe, an oscilloscope, and a voltmeter. That way you can compare the amperage draw of EACH BAR on the armature, the total amperage draw, the RPM of the pump motor, and the supply voltage. 'Course, most folks don't have an oscilloscope and low-amps probe.
As said, 9.5 is nowhere near enough; and cannot be accurate if you're showing more than that at your other pressure sensor.
Either the pump is faulty, there's a pressure leak in the fuel tank section of the plumbing, or the pump is starving for power.
