My '83 280zx non-turbo stutters after about 10-15 minutes from initial start up. The engine doesn't die and I can drive the car, but I get hesitation when I accelerate. I have made the following adjustments to each system listed below:

Electrical: I cleaned the battery terminals and ensured I had spark running the ignition coil. I replaced the ignition coil wire to the distributor. I cleaned the cap and rotor and also replaced the spark plug wires and spark plugs. I have spark running to the plugs so I feel confident that my problem isn't electrical.

Air: I replaced the old air filter with a K & N filter. I checked the vacuum hoses to look for any leaks and none were apparent. I do not believe the problem is air system related.

Fuel: I can hear the fuel pump running and working before I start the engine. I went ahead and replaced the fuel filter and checked the fuel lines for leaks in the engine bay. I am worried that I may have created the problem when I ran the fuel level too low which may have caused the engine to suck up debris from the fuel tank. As a result, I have only run premium fuel through the system and I add fuel injector cleaner every other fill up.

Engine: I replaced the oil and oil filter with full synthetic 5W-30.

I am not sure what I should look at next. Maybe a timing problem or flushing the fuel tank. My belts are also due for a change (not sure if lose belts could effect the timing). My biggest fear is that the engine may have an internal problem holding oil pressure as the oil pressure gauge drops close to zero when the engine starts stuttering.

Hopefully I described the situation correctly. Cars are more of a hobby for the time being so I don't have any substantial training or experience. Thank you for the help!