No start until oil gauge flickers

I have 1989 S10 4.3 TBI. It will turn over for about 10 seconds or more before it will start. As soon as the oil gauge flickers it starts. I have replaced the oil pressure switch. (the one that controls the gauge) same problem. You can hear the fuel pump run when I turn the key.
I know that the injectors are not firing until the oil pressure is picked up. This happens hot or cold !!!!!

Usually this will happen when the fuel relay is not working.
The oil pressure switch is designed as a backup to the relay. After the oil pressure reaches 4 psi (I think?), the switch will turn on and power the pump itself. It usually takes a long time cranking to get the pressure high enough to do this. Check that the relay is actually working.