They come with full 5w20 synthetic and many on this forum, including myself run synthetic. So whoever said not to put synthetic in a Hemi is nuts. As far as when to change going by either the manual or when your truck's computer tells you it is time will certainly work, although with some synthetics you can typically get more mileage out of an oil change than what the manual will state. You will not hurt anything by waiting for your first oil change until 8K or when the computer tells you to. Because it made me feel warm and fuzzy, and I am a throwback to the old days, I changed mine at 500 and then 1K miles, though I realized it was probably overkill in this day and age of modern engines.