The GX was redesigned for 2010. The 3rd row now only has 2 seats, rather than the 3 in the 2003-2009 models. This means that the maximum capacity is 7 seats starting in 2010. Beginning in 2017, the GX is now available as a 6 seater (with 2nd row captain’s chairs) – in addition to the 7 seater model (with a 2nd row bench).
It is VERY important to note that there are zero tether anchors in the 3rd row of the 7 seater model, and 1 tether anchor in the 3rd row (3P) in the 6 seater model. Why is this you ask? The government requires at least 3 positions to have tether anchors, so in the 6 seater model since there are only 2 seats in the 2nd row, at least one of the seats in the 3rd row has to have a tether anchor to meet the government minimum. Why on earth would Lexus not put a tether anchor in the 3rd row of the 7 seater version also… simply because they didn’t have to. Things like this are so irritating as on matters of a child’s safety we can’t understand why they cut corners and scrimp.
The GX was introduced for 2003 – and was available only as an 8 seater through 2009.
The lower anchors for 2D are overlapped into 2C making it such that a car seat installed with LATCH in 2D will block the use of 2C for anything else (car seat, booster or adult). The lower anchors for 2D are also on a hump in the vehicle in a way that will prevent getting a secure installation for a car seat there. Also, it is not possible to LATCH in a booster in 2D as the booster will sit on the buckle for 2D. The only functional position with lower anchors is the 2nd row passenger seat. If you need to install a car seat in 2D or 2C, you’ll need to use the seat belt (and if it is a forward-facing car seat, obviously add the tether).
The shoulder belt for 3C comes from the roof (yes, this is safe) – see here for how to use, connect, and disconnect this seat belt. Notably, all 6 seats in back have head restraints (including 2C and 3C) – this is impressive as many SUVs neglect the 3rd row and center seats in this regard.
The 2003-2009 Lexus GX has the same 2nd row as the 2004-2009 Toyota 4Runner (7 seater version). 
