96 gmc suburban 5.7 wont start when is cold

What is the fuel pressure, key on engine off and key on engine running?

fuel presure 55 pounds

Okay, is that the pressure with the key on engine off or key on engine running?

same presure key on and runing.

Fuel pressure is too low.

Could be a weak pump, a leaking pressure regulator, leaking injectors, leaking pulsator.

Try cycling the key on and off 4 or 5 times before starting when cold.

If this helps, first replace the fuel filter. If not, check all the fuel lines for leaks, chack the tank for leaks, ect. Charles