I have a 2010 R/T 6 speed that I bought in Sept. However it sat at the dealership since Nov. '09. I now have 1600 miles on it and want to change the oil. I know the owners manual says to run 5-20 but I am going to run Mobil 1 in it and need to know if the synthetic 5-20 is o.k. or should I go to 5-30. Thanks.