4 months ago, I picked up a 2004 F350 6.8 V10 from its original owner in california (29K miles). Truck was very well maintained and I have the service records from previous owner. I drove the truck home (2200 miles to Canada) and it didn't burn a drop of oil. Changed oil to PYB 5W-20 and ran that for 5000 miles (2months) and it didn't burn a drop. I then changed oil last month to Mobil 1 5W-20 and today i checked the oil with almost 4000 miles on it and its down 1/2 quart. Could it just be the Mobil 1? Should I go back to PYB?