The 2004 Chevrolet Suburban runs on flex-fuel (FFV).
It is in the fuel tank .
Fuel pressure regulator is located on the driver side fuel rail.
do fuel pressure test
Mounted on top and inside the fuel tank.
It doesnt have one outside of the fuel tank.
THE FUEL PRESSURE ON ALL CHEVY'S 95 AND UP IS 60 TO 65 PSI
No or low fuel pressure
Connect a fuel pressure gauge to the schrader valve located on the fuel rail that feeds the fuel injectors.
On the back of the block on the driver's side. There are fuel lines that go right over it.
Trouble code P0191 means: Fuel Rail Pressure Sensor Range/Performance
Then you have a BAD fuel pump. Replace the pump and filter. If it is higher then 63 LBS. then the fuel pressure regulator is bad.