Is that PCV valve adjustable? It could be way out of adjustment and letting pressure build. Also be wary of the liquid filled fuel pressure gauges. The fluctuate greatly with temp changes. Watched mine go from 10 lbs to zero and back to 10 and idled at zero for 20 mins. Drained the oil out of the gauge, rock steady 5.5 lbs no matter what the engine was doing.
