Since you do a lot of highway, If you plan on staying with mobil1, Id say to go with the 10w-30, or 0w-40. There is a lot of talk on this forum about 0w-30 being the thickest viscosity-wise when up to temperature and in the 30-range, but I think for your aplication, the minimal use of viscosity improvers (if mobil 1 does use them they will be the least in 10w-30, and if not, then you start out with a heavier base) is for the best. 0w-40 is good too, IMO, as the 40 weight oil will protect better, and youll get good flow at startup. (you cna find 0w-40 at autozone) Plus, even if viscosity index improvers are used, when the oil thins, youll be at a 30, instead of nearing a 20 wt oil, which is too thin for your engine.
I know running lighter synth oils in my 91 BMW, which is speccced for 15w-40 dino will cause a lot of consumption compared to heavier 15w-50 synthetics or 15w-40 dinos.
JMH
I just switched over to Mobil 1 0-30 at 36K miles from Castrol GTX 5-30 (currently have 38K). This is in a 2000 5.3 4X4 Silverado. I was changing out the Castrol at 2K mile intervals (this is before I discovered this forum). I have just about 2K miles on the Mobil 1 0-30 now and noticed that it is burning some. About an 8th inch down from the full mark on the dipstick. It has never burned oil with the Castrol. I plan on going with a 5K interval with the Mobil 1. My question is when I change this oil out should I go to Mobil 1 5-30 or 10-30, or just stick with the 0-30. I drive probably 70% highway, 20% country roads, and the last 10% stop and go. I will be doing some light towing in the summer.