Oil changes often?

When you change the oil, are you sure you are replacing all the oil filters? I know some trucks have aftermarket secondary filters installed, and I suspect that some manufacturers have secondary filter options.

Also, verify the viscosity rating your truck requires, and see if that rating is ambient temperature dependent. Run too thin an oil in high ambient, and the pressure may go too low. Run too thick an oil in cold ambient, and the pressure may go too high.

 

That could be normal. For my truck, cruising speed oil psi when the engine is fully warmed up is around 50 psi, and the idle psi after warming up is around 15 to 20.

If the issue is repeatable, you might try to get a mechanic to ride with you for a bit when loaded so they can hear/feel for themselves what is happening.

With your current clarification, I wonder if your oil pump might be preparing to fail.

 

What does the oil analysis say?

 

Do that before you throw money at it. Fuel will dillute the oil, making it thinner. An oil analysis will confirm if fuel is in the oil or not. Oil pump will not correct the potential oil pressure issue if that's the case.

 

At idle my D13 is 32psi with 1.28m . I would definitely be worried if I saw anything under 25psi. Is it throwing any codes?