First of all, would just like to say that I'm new to this forum and any advice will be greatly appreciated....

I have a 2000 Chevy 2500 2wd 5.7L. I went to get into my truck to go home and it wouldn't start. It cranks and acts like it wants to start, but just doesn't. A couple of days ago, while I was driving, the security light started flashing. Then when I went to start it today, the light would flash a few times and stop, but the truck still won't start. I ended up having it towed home and I've replaced a few parts today, but with no luck.
So far I've replaced the crankshaft position sensor, the ignition module, and the ignition lock. I read online about resetting the passlock for the security and did that, but it's still doing the same thing. I bought a fuel pump for it, but I haven't installed it yet because I can hear the fuel pump coming on and off when I turn the key.
It's not popping any codes, the fuses are good, spark plugs are good, battery is good. As you can see, I'm completely stumped. Thanks in advance for any advice

 

I know this is old but I was just going through this and was searching the INTERWEB nothing found it was my Coolant Temp Sensor unplug and you can check it it will start