I installed an Isspro fuel pressure gauge with isolator on my truck. After cranking up the truck it would operate at about 10 psi. When I turned it off, it would stick around 7-8 psi. I cracked the fitting on the gauge side of the isolator to bleed off the pressure. It worked fine for a couple of days. Now, it is sticking around 5 psi when I shut the engine off. I have the line filled with 50/50 anitfreeze mixture with no air pockets. Do I need to bleed it off again or does it hold pressure when shut-down? I am getting the reading off of the injector pump.