1995 Chevy Blazer Blazer rotates but won't start

Hi, I have a chevy Blazer 1995 4.3 v6 vortec engine. The car won't start unless I use starter fliud and have to keep pressure on the pedal or it drops and it stalls.

Acouple of codes came on and I changed the part. It was EGR and igintion module. I also just changed the coil maybe two months ago as well. I changed both, the fulel filter which was very clogged. I also checked the fule pressure aon the schareader valve and it was at 40 psi and changed the fuel filter. I then changed the fuel pressure regualtor and yet it is very hard to start.
So, I then switched the feul pressure sensors and it seemed to run a lilttle better, but I also noticed that I hear a ringing sound coming from the fuel pump with half a tank of gas.

So I am baffled what the problem can be.