My 1993 Chevy astro van 2WD 4.3L TBI 6 cylinder dies sometimes while I am driving usually under 30 miles an hour, when I am not accelerating and sometimes while I am accelerating. I replaced the fuel pump and the screen on the bottom of it, the gasket under the injectors. The fuel filter, and the battery. The spark plugs are firing right.

Why does it still die

Failing Ignition Control Module (ICM)?

When you start the van, does the check engine light come on, flash several times and then go off and stay off?
Have you had the Idle Air Control Valve (IACV) tested and/or cleaned?

I tested the ignition coil, the distributor and the ignition control module and they are all fine. When I start it the check engine light used to come on and off every couple of days and would go off. Its an OBD1 and when I tested it only the code 12 came up which is the OK code. Now since I made sure the battery terminal wires are all tight and reset the computer by disconnecting negative cable. Non of my lights on my dash come on immediately. The check engine light doesn't appear anymore, the anti lock brakes light comes on sometimes at start up and sometimes not for 10 or 15 minutes after I start it up. The spark plugs are firing correctly.

It seems that the van tries to die more often when it is just started up and when it is warm. When it tries to die, the oil gauge falls rapidly and I have to hit the gas pedal to keep it running.

Can I test the IACV at home or do I need to take it to a shop or autozone?

Testing ICMs with a Well's machine is virtually a waste of time. Instead, I recommend replacing them every 120,000 miles or 10 years, whichever comes first. I've seen many ICMs test fine that failed to work. Ditto for coils.

There is a specially designed harness needed to test the movement of your IACV. Most shops that do driveability work should have them. I would recommend doing a cleaning yourself first to see if anything changes as it probably will.
Get your hands on a good throttle plate cleaner and after the engine is warmed up and shut off, spray some into the throttle body and IACV and let it soak for a few minutes to work in.
Restart the engine (it will run rough at first and probably won't idle on it's own).
Keep it running about 1200-1500 RPM until all the cleaner burns out then repeat your road test. Hopefully, at least some of the symptoms will go away. Repeat if necessary until you're satisfied that any more cleaning won't improve matters. If it's till stalling/near stalling, have the IACV replace and consider also having the injectors professionally cleaned.

OK I found a relay to the fuel pump that was bad and replaced it, today now the engine is trying to kick on, but there is not any fuel coming up to the injectors.
I just replaced the fuel pump, filter, screen, had the wiring tested and everything was good yesterday, now today the fuel pump isn't even trying to pump. I listened for the whirling noise and nothing is happening. I cleaned the throttle body and it wasn't dirty. I replaced the pickup coil on the bottom of the distributor and we got it back in perfectly no problem there. I don't have a camshaft sensor or a crankshaft sensor. The fuel lines aren't plugged, but the fuel pump isn't doing its job.

Check all under dash and under hood fuses with a test light or multimeter.

I forgot to say this, but I also checked all the fuses.