when in doubt.. 10W-30. it's a one size fits all type oil. I live in a very hot climate (FL) and I just ru n 10W-30 Synthetic Mobil 1. I used to run 15W-50 Mobil 1, but went back to the thinner stuff. I can't tell the difference with either in my 3.0... so 10W-30 is plenty. Biggest thing you can do for your engine is :
A- DO NOT RUN FRAM OIL FILTERS!!!!
B- Run a synthetic motor oil (not castrol it's fake synthetic). A synthetic will allow the oil to flow in cold temps and when it's really hot it doesn't cook off. bang for the buck... Mobil 1 at Wal-mart. 5qts for $20.