Go with the Actron fuel pressure gauge. Also, it has purge valve so it is easy to discharge or relieve fuel system pressure.
I'd hold off on the fuel pressure regulator. Very seldom fixes the problem and turns out to be a waste of money but the fuel pressure test will determine whether it is flaky.
On the FPR, remove it from the fuel injector rail and inspect from the inside. One simple C-clip holds in on. Remove the vacuum line and look for fuel maybe indicating a ruptured diaphragm.
BTW - There are about 3 phases of checking fuel pressure. Initial check is at ignition to on engine off (fuel pump prime mode). Rest are with the engine running at idle and by removing the vacuum line to the FPR. You'll compare readings and see if within GM specs.
Actron Hooked Up to GM 3.4L V6