I convinced my Dad to start using Motorcraft 5w20 in his '02 Expedition 4.6. His manual says to change oil every 5000 miles, which he has done. He is on his 2nd change with the 5w20. While towing the boat to the lake yesterday, he looked in the manual under "severe" driving conditions. Towing is "severe", and the OCI should be 3000 miles. He has about 4000 miles on this interval. We are going to do a UOA. Should we change the oil now? Or go the full 5000 miles? There is probably about 1000 miles of towing on this oil change. The boat/trailer probably weight 3500 lbs. We tow with overdrive off. The engine just isn't big enough to negotiate the hills in overdrive. RPMs are about 2800 while towing. Total miles are about 28,500.