So yesterday my fuel pressure was at 15 like normal..and today got in my truck and started it up and still at 15..then filled up and notice while i was driving that it had dropped to 5...kept on driving and it rose ever so slowly(took about 200 miles) to 10 and that were it resides...any info thanks..

 

Is the gauge tapped in before or after the filter? If after the filter i would assume that the filter got plugged up with some bad diesel or something on that order.