How many of you have switched to synthetic oil? I contacted Nissan support and all they did was quote the manual with the recommended oil (i.e. according to the 2009 Nissan Frontier owner's manual, Nissan recommends using Engine oil with API Certification Mark *1 Viscosity SAE 5W-30). Besides the benefit of extended life, have you seen better performance, better mileage, less problems? My Frontier has 5000 miles so it's the right time to switch I think (break in period is over). I look forward to your insight!