Last oil change I put however many quarts it takes in it and check the dipstick marks , its right on the Full mark

 

My rear end and underside of truck is saturated .

 

So is mine, but my crank seal is blowing through about one gallon every 5K. Regardless, it sounds like you're leaking it.

 

Mine is leaking too...just not that bad. It's from the front damper seal. I tell my wife that it's a diesel...it's supposed to leak but that doesn't make her any less upset about the driveway. In MI, keeping the undercarriage well oiled acts as a rust preventative too!
I believe you have a leak but I'm just surprised with that much loss you don't have a pool in your driveway. Don't know if someone else mentioned this already but I wonder if it could be a blow-by issue that's pumping things out the vent when motoring but not so much when you're idling??