I don't know about the rest of you guys, but I find changing out the fuel pump on these trucks to be a major pain in the ass.
Why not just test it for flow and pressure before you spend the time changing the pump.
To check volume/flow, pull the fuel inlet to the carburetor and stick a rubber hose on it. The other end goes in a container - a beer can works.
Crank the engine for 15 seconds - with the hot wire to the coil pulled. After 15 seconds, check the volume of gas in the beer can. Anything over 8 ounces is well within spec.
To check pressure - without the hassle of teeing in a gauge. Just attach a gauge to the end of the same hose used in the volume test (0 - 15 psi gauge is plenty).
Reattach the coil wire and fire it up. It doesn't take hardly a second to get a reading on the gauge, so whatever gas is in the bowl should be plenty to check the pressure. If you need to, you can keep it running for longer with a can of ether. If you get at least 5 psi discharge pressure you are good (factory spec is 4 to 6.5)
If the pump fails either test - and this apparent fuel flow issue has only developed since the new pump was installed, check your pump suction hose for pinch points and also check the steel discharge tubing for a kink. If your piping is okay, bring the pump back to the parts store.
If the pump passes both the volume and pressure tests, look to the carburetor as the problem (specifically, the bowl float not opening wide enough).
