I have no oil pressure 1996 chev 2500 - 2006 Chevrolet Silverado 2500HD 2WD

It's a process of elimination change it

try adding some valve & lifter top oil to your oil.
If you ever take the oil pan off, remove the oil pump pickup screen and clean it. You can also try a lighter weight oil.
If you take the VIN number to your chev dealer parts dept they can tell you which transmission you have....for free.

there is a daytime running light module bolted under the dash to the right of the steering column

it's located at the rear of the engine right by the distributor. There's a special socket to remove the switch. It won't be in very tight so you might be able to use pliers or vice grips if you can gain access. Let me know.

On the v-6 engines the oil pressure switch feeds the fuel pump. I'm not sure about your 1500. You didn't say what engine you have, so I will assume it is a v8. The oil pressure switch should be behind the distributor, near the firewall. You can use a paperclip as a jumper in the electrical connector that goes to the oil pressure switch. If it's the switch or low oil pressure, the jumper should complete the circuit and energize the fuel pump.

yes it set a code that can be retrieved with a scanner. it could be one of several sensors

Whe you turn the key to the on position you should hear the fuel pump working for about 5 seconds. If not replace the engines oil pressure switch for the fuel pump is linked to this part. Once the engine reaches normal operating oil pressure the computer shuts the circuit off to the third wire from the oil pressure switch which is linked to the fuel pum feed and the computer then turns on the fuel pump relay to operate the pump

Does the oil light come on or the knock occur during the engine warm up after a cold start?
There could be a couple of problems causing the issue. You could have an oil pressure pump or pump pressure regulator sticking. I would have a mechanical oil pressure gauge installed and verify oil pressure at idle and 2500 rpms to make sure oil pressure is in normal ranges.
You could also have excessive piston rod bearing, crankshaft bearing or cam shaft bearing wear that will cause oil pressure to drop too low to prevent the rod knock your hearing at 2500 rpm.
You said a knock and not a ticking noise,so I don't believe a lifter is the issue at 2500 rpm.
Start with the oil pressure check and go from there.
Let me know.
Regards,

Just to add, hope this helps with sensor location. The spec I saw was 30--80 psi oil pressure at 3000 rpms. In the old days they used to say for generic spec, 10 psi for every 1000 rpms. Always use the proper spec. You might be able to use analog pressure gage to screw in to replace sending unit to double check oil pressure. Just my opinion.

It could be the pump running but not achieving enough fuel pressure. It needs to be at least 55 psi.