I am loosing pressure after priming the system the vehicle cranks but wont start.

Sounds like you are possibly loosing fuel prime. One easy way to confirm is to cycle the key a couple of times in the morning to prime the system before trying to crank the engine. If it starts better then you have confirmed that the fuel system is loosing pressure when the truck sits. From here you have to determine if it is a bad pressure regulator or a bad injector letting fuel bleed by when the engine is off.

Without knowing the vehicle a fuel injected car all you have to do is turn the key on and off 3 times for 10 seconds each. Carburetor is a bit harder. If the system does not leak cranking it can get it done but dumping a little gas in the carb will cause it to start and pump the manual pump much faster to prime the system. With a leaking manual pump it just takes a lot of cranking.

That system is self priming, my first thought would be crud from the bottom of the tank got stirred up due to low fuel, and some small microns of dirt got sucked into the system and took out your fuel pump. Dirt naturally gets into everybody's tank, nothing you can do about it. My first try would be to cycle your key a few times to purge the system, not to many though as yes fuel injection can and will flood, if that happens to clear it out hold your foot to the floor till it starts then back to normal. Dont over rev you engine. Another thing to check is to remove the vacuum line from the fuel pressure regulator and smell it, if it smells like gas then the pressure regulator is bad, common issue.
But this wont keep it from starting only makes for a long start and lower fuel economy. Hope this helps.

I can't look up wiring diagram w/o year--make--model? Usually if it cranks good but won't start, have a helper crank it while you visually check for spark at the plugs, where applicable. If spark everywhere, use a gage and check proper fuel pressure. Also, check fuel injector pulse.

My automotive database is a US database, it won't have vehicles sold only in other countries.

fuel pump is loosing its prime.. sometime the check valve that holds pressure in the line fails and the fuel returns to the tank.
this is why you have to turn the key on and off to build the pressure in the line back up.
fuel injectors require a certain pressure to open and with out that prime in the line it won't start
things to look for are leaks in the fuel system or replace the pump.. but some cheap pumps will cause this problem from the day they are installed

This sounds like a fuel system priming issue. When you first turn the key to the ON position (not cranking yet), you should hear a three-to-five second buzzing noise. This is the fuel pump running to pressurize the fuel system for cranking. This is controlled by the PCM and is relay activated. Once the vehicle starts and oil pressure rises, then the fuel pump is activated by the PCM via a different relay. If you can't start at first, what is probably happening is that the prime is not occurring and you have to crank it until the PCM sees oil pressure and then fires off the fuel pump. It could be PCM wiring or a bad fuel pump prime relay.

There is a separate circuit and relay that primes the fuel system when you start the vehicle. If you sit in a silent location and turn the key to the ON position (without cranking), you should hear the fuel pump run for about 5-6 seconds. This is to bring the fuel pressure up in order to let the vehicle start. Then the normal pump circuit takes over. Sounds like your priming circuit is not working. I would try the relay first.

Most vehicles have a "system prime" that occurs when the ignition key is moved to the "ON" position. This is where the key ends up after you start the engine. This prime runs the fuel pump a second or two to get the fuel pressure high enough for the injectors to work once you crank the engine. The prime is performed by the fuel pump relay. In a quiet area (minimal noise, no radio), sit in the vehicle and turn the key to the on position without cranking the engine. You sgould hear a 3-5 second buzz or hum. This is the fuel pump coming up to pressure. If this is not occurring, then either the relay or the pump is most likely bad.

I take it you mean it WILL crank(turnover) but wont start. Anyway, Your problem may be a lack of fuel pressure. Could be the filter is now clogged. Trapped air in fuel lines, and fuel rails. Most GM vehicles have a schrader valve on one of the fuel rails. It looks similar to a tire valve stem. You could turn the key to on, make sure you hear the pump in the tank running. It will run a few seconds to pressurize the fuel system, and run continuously after the engine starts. Using a fuel pressure gage to check pressure and depress the valve carefully to visually see if fuel or air is present. Dont position yourself to be sprayed with gas.

Most late model vehicles wont arm the ignition(spark) systems unless there is correct fuel pressure, among other things. Something you may not know is that most all fuel tanks have a reserve of 1 to 3 gallons of fuel in the tank that wont register on the gage. Putting in 1 or 2 gallons most likely is not enough to prime the system. Hope this helps.

This vehicle needs 65 to 70 psi fuel pressure.to start cold, it will run with 55 after priming