I'm a new member from North Carolina and drive a 2001 F-250 CC 5.4 with 67k. I've spent the past week reading every post on this board and have decided that I am going to switch to Mobile 1. The book says 5w-20. Should I go with 5w-30 or 10w-30 M1. Most driving is combination city/hwy. We do pull a 3500 fish boat when we can-mostly in the summer. Switching viscosity from Summer to Winter is also an option if advised. Thanks for the help-this is a great resource!