Truck has 220,000 miles. Run Delo 15w40 with Frantz by-pass (2k element changes on the Frantz) and Stratapore main filter.
Last year I started a long term test with 5k sampling. Each time oil came back good to continue running, no unusual numbers on anything.
I finally changed oil and the Fleetguard filter at the 1 year mark with 23,000 miles on both the oil and Stratapore filter and sent in a sample, again everything good to continue running.
I did add about 4 qts of make-up oil over the year which supplemented the additive package and the Frantz kept things clean.
While according to the analysis I could have continued without a change, I just felt better changing the oil at the one year, 23k mark. I'll now likely stick with a annual change with one 10k analysis, then change at 20k.
I did do one analysis on the wifes 98 on a 10k change and it too came back good to continue running.
I'm convinced that many change oil (and filters) far more often than necessary, but their money and truck.