I live in LA and have a 4.8is and would suggest listening to the previous suggestions...I also drive up to Tahoe quite a bit and picked up a set of 18" snow wheels/tires this past summer...The 20's up in Tahoe are going to be completely useless, not to mention that if its snowing when you get up to Kaibers pass, they won't let you go through chains or no chains. Not only are these tires too wide, but when coupled with the 4.8's stump ripping power, I'd be surprised if you even made it a few inches in that heavy crud up in LT. Even with my brand new blizzaks, the 4.8 is constantly trying to stay hooked up. Also keep in mind that they have gotten 7+ feet of snow in the past couple weeks, you will most likely encounter a side road that still has 2 feet of snow on it unless you are driving straight into heavenly village and not leaving it.

Best car I ever drove in the snow(20years of snow driving) is still the old ass subaru station wagon 4x4 we had with 15" tires...that thing was absolutely unstoppable and had probably 90hp to the wheels! Haha