1997 F150, 4.2 engine, 80,000 miles

I've had the upper & lower intake gaskets replaced 3 years ago.
This spring my oil guage would go all over the place and the check engine light would come on, i stop the truck and check oil, OK.
Start up truck & everything is just fine.

This happened 2 more times, same thing everything fine. Always seems to happen after highway travel (15 mile trip).
I have kept a close eye on the oil level.

Then was getting ready for trip, decided to check oil level before i left.
NO OIL WAS SHOWING ON DIPSTICK. Put 2 quarts of oil in to fill to line on dipstick. (2 quarts low). No external leaks, must be going through the exhaust.
Was sick to my stomach, so it has been parked ever sinc.
I haven't driven it yet (that was in May)
I feel that i need to cash in my losses (ie. trade/sell while i can)

Any ideas on what it is? Did i ruin my engine?
I am trying to talk myself out of buying new truck.

 

Have you ever changed the PCV? I would pull the plugs and do a compression check.

 

I plan on putting in new pcv this weekend. thanks