I am currently running Mobil 1 full synthetic in my 2019 silverado with a napa gold oil filter. I have been sticking to the 6 month drain interval. I do short trips most of the time. I am also a volunteer fire fighter and occasionally the truck sets and idles for a few hours (rare but it does happen). By the time 6 months is up I have maybe 3000-3500 miles on it. I know you can go easily 7000 miles on this oil but with the short trips and the occasional idle hours am I right to change it the way I have been or am I just wasting money on oil?