Quick question... I'd like to switch to synthetic oil in my 2001 Chevy Z-71 at my next oil change. Any special steps I need to take when switching? Do I need to purge out the old oil, or is it a standard oil change and just add the synthetic? I run 100% synthetic in my Harley, but I've always had it serviced at the dealer, so I don't know what they did when they switched. Also. the 2006 GTO's come with synthetic (mobile 1) correct? Thanks in advance.