I did not buy my 4runner because of the roll down rear window but I loved it in my 3rd generation vehicle and my dog loved it as well. Problem is I seem to be very sensitive to carbon monoxide. No kidding, a while back everytime I would get into my daughter's car and ride with her I would feel nauseated within 3 minutes. No one else felt this way but me but I had her exhaust checked out nonetheless. Turns out there was a very small exhaust leak. Once fixed I no longer felt ill when riding with her. Well, although I did not experience this particular exhaust problem for unkown reasons with the 3rd gen, each time I roll down the rear window in my 5th gen, even slightly, I get that same sickening, nauseous feeling after 2 or 3 minutes. I've seen the other thread in this forum regarding this problem and I've tried opening some of the other windows, etc but it doesn't seem to help much. So really, for me, unless my TE is stationary, I, or rather my shepherd does not reap the benefits of driving with rear window open but, he seems to be happy hanging his big head out the side window!