I checked out Mobil1's site and it says that we can use 5w-30, standard, extended performance, or truck & suv for their "ultimate" level of performance. I used to use only Amsoil 2000 Series 0w-30 and was extremely happy with it, but I've since switched to Mobil1 (which costs me about half what I was paying for Amsoil) and I haven't noticed any degradation. I've used both standard and truck & suv formulas.
Calmini Cone Air Filter, PowerVault PV2 Muffler, OME Trooper Springs, Rancho RS9000X Shocks, 285/75R16 Nitto Grappler AT's, Pioneer DEH P8000R In-Dash CD, Amps and Drivers Built by Orion, Wires and Fuse Blocks by KnuKonceptz, Vibration Damping by BQuiet, Alarm System featuring Auto Start and Remote Windows, Yakima LoadWarrior w/Full Size Spare, Debadged/Custom Titanium Grill Logo, Tint (5% Rear / 20% Front), Steel Braided Brake Lines, G2 Painted Calipers