My brother-in-law saw his first SSR, mine, last weekend and suggested I switch from regular oil to synthetic oil in my SSR as it would last longer and give me better gas milage. Is this true, and is it safe to go from regular 5W-30 pennzoil to 5W-30 Mobil 1 Synthetic oil? Is the 5.3 designed for synthetic oil? Would I have to flush the system before installing synthetic oil? How do you know when it's dirty, and how often do you have to change synthetic oil?