Ideally you probably want to check it with a T fitting right near the carb at idle, but a "deadhead" connection will work too. 9 psi is too high though. This is a big problem with modern manufacture pumps.

The fuel pump output is a critical because everything else depends on it being correct, in particular the specific fuel height in the carburetor bowl must be maintained at all times under all conditions. The float and bowl sort of looks like a toilet tank but unlike a toilet the fuel level doesn't rise and fall.

maybe this one?

The float does ever so slightly. The fuel level stays constant or nearly so, by design. That's the idea, anyway. Very common misconception! I know, cuz I had it too. The reason is because the carburetor is calibrated to have this fuel bowl level maintained very closely. Some specify wet fuel height to within 1/32", they wouldn't do this if it wasn't important. So everything factors, fuel pump pressure, the weight of the float, inlet orifice size etc. Remember the fuel level in the well rises to the same height as in the bowl. The air flowing through the carb draws it from the well, called pullover. If you've ever tried to siphon gas from a full container versus one only a 1/4 full, it's easier to get a full container started. it's kind of like that in a way.

"Similar to the float in the tank of a toilet, there's a float attached to the needle valve in a carburetor. The float rides up and down with the level of fuel in the bowl and acts on the needle valve. Unlike the tank in the bathroom fixture, however, the goal of the carburetor float, needle and seat is keeping the fuel level constant in the bowl, regardless of the demands of the engine. The carburetor float bowl does not empty and fill as the tank of the bathroom fixture does."

https://www.hemmings.com/magazine/hcc/2015/02/Bowl-and-Float-Assembly/3746461.html

Don't even have to start the engine. Just crank it over with the ignition disabled for 5 or 10 seconds will tell the tale.

I think the fuel pump is actually defective from the numbers you describe. The shop manual for your truck lists the fuel pump pressure spec. Find out what it is. I bet it's 4.5 to 5.5, something like that. All things being equal, I'd rather have a mechanical fuel pump that is within the factory spec, vs. trying to tamp it back down by half with a dial regulator. Have you checked the pump for volume?

It's possible, even though the unit has nearly twice the fuel pressure output spec, it is unable to supply sufficient fuel volume under high demand. A pressure regulator won't remedy that.