I have a 2001 Tahoe that I just got back from a transmission shop with a new remand tranny in it. but now it wont start. it'll crank over but wont fire up. when the key is turned to on you can hear the fuel pump prime for about 3-5 seconds then it stops. I turn the key to start and it just cranks. I've also replace the fuel filter and fuel pressure regulator and still no luck. it has 52psi at the shredder valve when you turn the key to on but then starts to drop. Could it be the fuel pump even though you can hear it prime?

 

Just because you hear the fuel pump running, it does not mean that it has the correct fuel pressure. It could be high for a few seconds and then drop off. You can spray a little bit of gas or starter fluid down the throttle body and if it runs for a few seconds, it ius the fuel pump.