the only "test" for a regulator is to check fuel pressure key on/engine off, then with the car running. The fuel pressure should be 41-44 psi KO/EO, and should drop 3-7 psi while running at idle. Disconnect the vacuum while it's running, and the reading should return to close to KO/EO readings.
There is no easy way to check which injector(s) are the problem other than to pull the plugs (no easy job either on a 3.4 DOHC) and see which ones are most fuel flooded.