I second Mike's idea of gradually switching. Start first with semi and if your engine doesn't show signs of leaks, switch to full. I generally think synthetic oil is for high reving/turbo engines. Where the oil gets really heated up. Personally for a V-8 as large as yours I would just stick with the "change it hot and often" principal, using a good conventional oil such as Castrol GTX. It's really a personal decision, what ever makes you feel comfortable.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member