Message: I just got my truck 'bagged and I've notice that when I go to lift the rear when the front is already lifted, the front bags lose pressure (around 10-20 psi). I have SMC 1/2" fill valves and 3/8" dump valves with a 5-gallon tank at 150 psi. Is this normal, do I need check valves?? Any help would be appreciated...