Cooper993 wrote:I do 6K but I use Mobile1 full synthetic
ditto.
I had an oil analysis done on Mobil 1 5W-30 after 6,000 miles (truck had 17k at the time) and it showed that it could probably go another few thousand, based on the TBN. Now I have 53k miles, and I'll probably take my next oil change to 7,500 and do another analysis.
The only way to know for sure is to have an oil analysis done with your oil, your truck, your driving habits, and your environment. I'd recommend Blackstone Laboratories.