I don't think that's the gauge actually showing "pressure." I think it's one of those preliminary check deals when you first turn the key and all the gauges move and then fall to 0 kind of thing. There clearly isn't pressure if you're not cranking. Could be a fuel pressure issue too. Pump might be weak causing not enough pressure to fire the truck, but as you leave the key on the pump keeps building pressure and finally you have enough to get the injectors to fire some fuel and get the truck started. Anyway you can hook up a simple mechanical fuel pressure gauge and get a reading?

 

My truck does the same thing 03-6liter I think its in limp mode but don't know wat to do either

 

try pulling the IPR. Check the screen on the end. Ive seen the IPR cause a concern like this. Normally not with a no start but its possible.

 

Yeah did that allready no luck

 

Start a new thread and give us some more info on the truck please! Welcome to DB!