Another thing you should check is whether or not you have engine sludge. Look under the oil fill cap. If you see a buildup, you need to get a serious engine cleaning or you'll loose the whole engine. I'm currently trying to have the engine in my sisters 2000 XLE replaced. The sludge built up and caused one of the cam shafts to snap. It will need a new head just to get it running, but who knows how much stuff is built up inside other places. If you engine gets sludged, Toyota is very good about taking care of you. Just be sure to get it there before you lose the engine. Also, be sure to save your oil change receipts. My sister lost most of hers and I've been struggling for a week now to come up with a sufficient paper trail. Toyota just doesn't consider her log of dates and mileage for all maintenence that she kept in a spiral notebook to be sufficient. Imagine that.