What is the minimun fuel presure needed at idle? mine is fluctating between 4900 to 5100. Just had new injectors installed, there is now a miss at idle.

is it a miss or a rough idle? A rough idle is signs of a FPR going out. Fuel Pressure should be close to what desired is, it shouldn't jump around at idle.

Seems like a miss, right now it is just intermitted while at a stop light it will miss once or twice then idle good. Then after a few seconds it will do it again

Fuel pressure regulator. Honestly my rail pressure fluctuates too at idle so changing the regulator may not make a difference. You should log the pressure while driving.

You can determine the difference in desired and actual. Also if your truck has mods, it is normal to idle differently.