1991 Chevy Truck fuel pump

With the engine turned OFF, relieve the fuel pressure at the pressure regulator.
Disconnect the negative battery cable.
Raise and support the rear of the vehicle on jackstands.
Drain the fuel tank, then remove it.
Using a hammer and a drift punch, drive the fuel lever sending device and pump assembly locking ring (located on top of the fuel tank) counterclockwise. Lift the assembly from the tank and remove the pump from the fuel lever sending device.
Pull the pump up into the attaching hose while pulling it outward away from the bottom support. Be careful not to damage the rubber insulator and strainer during removal. After the pump assembly is clear of the bottom support, pull it out of the rubber connector.

To install:

Connect the fuel pump to the hose.

Be careful that you don't fold or twist the strainer when installing the sending unit, or you'll restrict fuel flow.

Install a new O-ring on the pump assembly and then position them into the fuel tank.
Turn the locking ring clockwise until its tight.
Install the fuel tank and connect the battery cable.