There is slowly growing evidence that some 4.0L Toyotas are turning up with head gasket issues at just over 100k miles.
I have a 2006 4Runner that may have this problem right now. It is not catastrophic failure, but will worsen over time and require repair. Average cost for the repair is running right about $3,000 for those who take it to a shop.
Do an Internet search for terms such as "Toyota 4.0L head gasket", "1GR-FE head gasket", etc., and you will find cases. I'm not sure whether the problem will grow as more of these motors rack up miles, but it's not a good sign.
Otherwise, the vehicle has been a beast. The 4.7L V-8 in the 4th Generation 4Runner is one of the better motors available anywhere.
