how fast can you drive in 4wd mode

Typically you can shift into 4WD at any time but optimum speeds seem to be less than 35mph. As far as driving in 4WD, highway speeds of 55-65mph typically aren't excessive, unless conditions prohibit safe driving at that speed.

Don't drive it over about 40 in 4x4

dont shift into 4 wheel over 35 migh damage the transfer case... as for top speed you can go as fast as the truck will go in 4 wheel...as long as your going straight when you turn in 4 wheel mode it put alot of strain on the transfer case if your on dry ground and the faster you go the more strain until boom- no more tranfer case

I have a 2006 4Runner Limited 4.0l V6. The manual says you can shift to or from 4WD at up to 60 MPH. Personally, it makes sense to me to limit this to under 35 MPH, which I have been doing for 15+ years on my perfectly maintained 4Runner. The MORE IMPORTANT thing to do is to run in 4WD at least 10 miles per month, as recommended in the manual. This will keep the mechanical components lubricated. I've seen many failures by owners not doing this simple precaution. This is a GREAT SUV and deserves extra TLC. I have been offered more than $6,000 over top retail price, but I just can't part with it.

Fast enough to kill yourself. You do know 4WD does not add traction to the tires? Driving fast in slick conditions is dangerous.