Sudden loss of MPG

[c7train]

I have a 2007 E350 V10 with 109k on the clock. We got it with 48k miles and was getting over 12mpg all the time, maybe 13-14 (better at sea-level). This last trip I got 9mpg. Has anyone experienced anything like this?

Both valve covers have oil on them so I checked the PCV valve idea, but it rattles just fine like it should, although it doesn't seem to seal all that well to the valve cover. The passenger side valve cover has what appears to be the "heated" PCV valve while the driver's side just appears to have either a regular PCV valve or just a grommet and hose coming out of it. Ideas here?

Also, I have the little puff of smoke on start up but it's very random and hardly ever happens. Thoughts on this? The van runs great and doesn't seem to use any oil. No check engine lights are on either, I have it chipped from 5 star tuning, would that effect check engine light not coming on?

Any help on this would be much appreciated, we are heading out on a trip for The rest of December and start of January and It would be nice to get the "regular" MPG again.