Hard to start

I have a 2000 GMC Sonoma ZR2 that is hard to start when cold. I have replaced the ECT sensor and fuel filter. Have recently had sending unit part of fuel pump replaced. Fuel pressure checks out fine at 50-55 psi. Checked plugs, distributor cap, rotor. Seem fine. Fuel pump can be heard operating normally. Turns over for a few seconds, starts, dies immediately before it can reach idle. This happens anywhere from 3-5 times when the engine is cold then it will finally start. Once it is started, I can turn it off and it will start just fine. Truck runs fine. No miss-fire. Happens in cold or warm weather. Please help.

50-55psi is low. 54-60ish psi is where is should be. This could a weak fuel pump, a weak regulator, weak battery/low charge, could also possibly be a partially clogged fuel filter. First on the list would be to check the battery with the engine off and see what the battery is holding at. If that checks out, when was the last time the filter was replaced? Hope this gives you an idea.