Synthetic 5w50 Schaefer oil

Dartish said
Mild, hydraulic flat tappet 360 in a truck that sees ALOT of mud and snow. Sustained load and rpm while toying around get it warm now and then. More interested in longevity then every last horsepower. I've liked the 50 weight and this stuff sounds like a decent oil and flows quicker then the dino oil when it gets cold in the mornings

Then you are a good candidate for a very high zinc oil. Test a sample new and then test again every 5000 miles or so and see how fast you are using the additive package. Then you'll have your drain interval.