I have some problems with my fuel system

Have the computer scanned for codes. Run a compression test. According to my reference material, the fuel pump on your truck is an in-tank model, so I'm not sure what you mean by "4.The copper tubbing located on the top of the fuel-pump assembly has also been re-fabricated due to the copper tubbing had a very big hole and a little hairline cracks". This is part of the fuel system. If it fails, it should be replaced. I'm going to presume that you are talking about the fuel delivery tubing on top of the tank access cover.

Hey rivermikerat let me take this one, Hafa Adai are you in the island ? or I got the wrong no. if you're talking about it sputtering there's a lot to it-Try doing everything I've mentioned below asap and give me results and send it in PM and we'll fix it thru there.I'm here in Dededo -dunno about you and also being a chamoru-let me know

No problem Raz, but you didn't give him any diagnostic steps.

Thanks Mike, Oops! I stepped on it they we go:https://www.2carpros.com/articles/engine-hesitates

Could be caused by one of the following below

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard it and keep testing.

Thanks alot for your response to my letter... But you wouldn't think that it could also be the (Mass Airflow Sensor,or the Map Airflow Sensor)One of the two parts mentioned above could be out ? It starts up really well it's just that when i apply my foot on the accelerator pedal and have the red needle reach 2000 rpm thats when it will start to spotter.It sounds like as if the gas is starving when it starts to flow into the carb or whatever the real name of that area is really called.It also makes that noise where when i apply my foot on the accelerator the gas tends to sound like it is starving for gas to flow right.. Like wise i've had (2ea.)certified mechanics trouble shoot my motor and both said that it is common that the (mass airflow sensor as well as the map airflow sensor )they both tend to go out fast within the 1990-1997 Nissan Hardbody..It could be driven but as soon as i give it in maybe @ about the speed limit of 25-30 miles per hour the truck tends to spotter where the compression and the drive of the truck is really weak on as far as gas coming through.... ?????