Here is my problem, about 2 weeks ago truck is getting very hard to start.
I have done the following. Fuel pump was replaced one year ago. Fuel filter changed yesterday and was plugged. Checked computer and there are no codes, but replaced temp sensor anyway. I've checked the fuel pump relay and can hear and feel it when key is turned to the "ON" position. I just checked the fuel pressure with a reading of 50psi with key in the "ON" position, after 5-6 tries of cranking and engine comes to life it reads 55psi.
Once engine is warmed up there are no problems with starting, or performance. Any help much appreciated.

I don't have my manual handy but it sounds like there isn't enough fuel pressure, how do you know the filter was plugged ?
And if its big stuff stuck in the filter, your pump is also probably plugged, there should be a plastic type strainer on the inlet but it may have come off.

If the problem goes away when the truck warms up, its more likely igntion, like a distributor cap or rotor or wires, etc.

I removed filter myself and could not blow through it. I'm leaning towards the low fuel pressure that you have indicated. If I cycle the ignition 4 times without cranking engine I see pressure rising to about 61 psi and seems to start with no problems. I will try this again first thing in morning when outside air temperature is cool again

if your pressure drops fairly quicky after the pump quits it could be a fuel pressure regulator.