Isx 15 mpg dropped 1.5 mpg

[Breeze]

Hey guys , my single cam 2013 isx dropped 1.5 mpg over night , demandated a year ago, and no real running issues to speak of , just lost mpg, was showing a low rail pressure code and replaced fuel filters to fix that , so no more codes , new cam and rockers 200,000 ago , and no real black smoke i can see , but she is a grass burner , and i see no external leaks , any ideas ? Its hard to trust anyone out here , and im way too far from jerry to get to him for a few weeks ,