I asked this in another thread of mine in the 6.0 Engine and Drivetrain forum. Just bought Delo 400 XSP 5W-40 synthetic since the Delo 400 LE 5W-40 synthetic seems to be discontinued. The XSP is the CK-4 rated but says it is fine for the CJ-4 rating and all other applications. I'm assuming it's okay to use in the 6.0 but I'm not the expert. I'm due for an oil change in a couple hundred miles and wouldn't mind knowing for sure. Any thoughts or evidence?