Monday I changed the oil in my 2k3 Durango 4.7 with 144,000+ miles. This time I decided to use up the last of my Lube Control. I added 3/4 quart of LC, 5 quarts of Castrol GTX 5w-30 and 1 quart of Castrol SYNTEC 10w-40. I plan on extending this oil change to 6500 miles. I would like to know if I should stay at the 5000 mile change or would the 6500 be OK? Right now she is purring like a kitten. I plan on 300,000+ miles out of this truck. So far so good! Oh, I drive 100+ miles a day. 99% highway always.