6'4'' here, and we have the following T4Rs:

3rd Gen w/ sunroof
4th Gen w/o sunroof
1st Gen GX
2nd Gen GX


I can't fit in the 3rd Gen 4runner. With the seat adjusted to nearly a gangster lean my head still brushes the headliner. I ride in it as seldom as possible as a result.

the 4th Gen w/o sunroof has plenty of headroom with the seat all the way down, but the slope of the front of the roof still makes it feel like I am sitting just a tad high with respect to the windshield. This is a subjective issue, but bottom line is, 4th gen w/o sunroof has sufficient headroom.

1st Gen GX - gobs of headroom. I think the GX is advertised as having 41", and you can tell. The higher roof line also makes for a better vertical line of sight through the windshield and makes the overall experience feel less cramped.

2nd Gen GX - My concern before biting the bullet on this was that its 38" of advertised headroom would be insufficient. After sitting in one, I can confirm it feels like I have just as much headroom as the 1st Gen GX, despite it supposedly having three inches less headroom - so there you have it. It feels like the 2nd Gen GX's seat can adjust down lower than the 1st Gen GX's, which may be where the headroom comes from despite the 2nd Gen GX having a lower roofline.

The 2nd Gen GX also feels much bigger on the inside than the 4th Gen T4R/1st Gen GX, and I suppose that's because it is - definitely wider, so it feels less cramped when you have someone in the passenger seat.