At what point can I switch to synthetic oil on my new Tacoma? It's got the 2.7L I4 engine. The dealer said it isn't broken in until around 10,000 miles. I've got 5000 miles on it now, having change the oil at 1000 and 3000 miles, w/the next one scheduled for 6000 miles. I plan on going w/the Amsoil series 2000, if I can get any, or Mobil 1. Thx.