[brown7373]

I would drain the oil and change the filter and use 10W30. I don't think the additive is that important with an already broken-in cam running stock springs. New cam break-in, especially with heavier springs is a different story. But it's not that expensive if it makes you feel better. I would change the oil and filter a second time, after it runs for a while, because you will drain cold oil that all the junk has settled out and been sitting for 5 years. After the initial start, the new oil will be hot and the junk that was on the bottom of the pan will then be drained out with the 2nd oil change.

Also drain flush and replace the radiator coolant. You need to check and replace the hoses which may be weak. Same with brake hoses, which often deteriorate from the inside out. I would doubt that a truck that sat for 5 years has recent brake hose replacements.

After you get it running, you can check and replace brake components as needed