0-40 is good. If you're truck has 60 to 70k mi and you live in the south like me 50 wt will be good for summer not winter. It's too thick and won't travel the engine well under a cold start. My motor has 12kmiles and I run 30wt. And royal purple is the brand of choice. Or To save a buck it two castrol super bike formula is really really awsome oil. But can't go wrong with royal purple I've seen a hands on test that couldn't be manipulated that has me sold!
Ive responded to a couple of your post, and i dont want it to seem like im attacking you, i just want to make sure you are properly informed.
The higher the number the thicker the oil, that is correct. The lower the number the less wear protection and "thinner" the oil. There are polymers in motor oil that cause it to "thicken" up when hot, unlike vegetable shortening or cooking grease. There are also Pour Point Depressant additives (VI) that keep it thin when cold.
We not only have a considerably close tolerance engine, but like you said, it is also long, and the oil channels are small and Loooooong. The thin when cold oil allows it to quickly get to engine parts when starting to keep it from running dry. So where your wrong is a 0w15 and a 0w40 is verified the same viscosity when cold. The 40 weight is thicker and more wear protection than the 15 when hot. Others and myself run a 15w50 as it is a slightly higher performing oil, with more friction modifying additives (VI)
The only drawback is you must allow more time for your engine to warm up after starting. Do not rev it until it settles rpm, and do not drive off until the oil temp gauge moves. Unless you have rebuilt your engine with bearing and piston ring tolerances looser than stock and have different lifters you should NOT be using a straight 30 weight oil. 30 is VERY different than 0 or 15 when cold!
We also have what is called a Fast Bleed Hydraulic Lifter. If is a compressible lifter that absorbs some of the cam lift and duration at low rpm, improving idle quality, low rpm tq, and emissions. It does this by filling with oil, and by way of a small orifice hole, squirts oil out of it and shrinks in size, effectively shrinking the percieved lobe of the cam. This hole diameter was designed by the engineers with the consideration of the oil viscosity recommended for the engine. A thicker oil will not evacuate the lifter as quickly and increase the valve lift, causing the engine to idle and perform differently at idle and low rpm. My 15w50 weight has a considerable change in idle quality as compared to the 0 weight. I can tell this as i am running headers with cutouts.
Finally you should NEVER run Castrol Superbike oil OR ANY OTHER MOTORCYCLE OIL! The 5w40 is similar to our oil, but it has certain wear additives that are damaging to your catalytic converter and O2 sensors. Motorcycle engine oil does not contain the friction modifiers of a passenger car engine oil (put in place for fuel economy in cars) and as a result will cause dramatically accelerated wear, Because motorcycles have wet clutches. Motorcycle engine oils shear (breakdown viscosity) more quickly than regular engine oil. Likewise you never put Car oil in Motorycles. You will ruin the clutch.
If you insist on using oil that is not listed on your oil cap, run Rotella or Motul. Primarily used in diesel engines that have LONG oil change intervals, they have a ton of detergents to keep it clean, extra friction modifiers and more shear resistance. Dont get me started on Royal Purple. Lets just say it is NOT what it used to be.