I got my OT this February. Build date shows 12/24. It's registered as a 24. With 3,500 miles on it so far, no breaks squealing, no engine problems, paint is perfect, no reboot of the ET system while driving, smooth driving however not as smooth as my other GX's. I changed the oil recently and not much metal in the oil and the filter was really clean. I do have the slight hood flutter which doesn't bother me but I will ask Lexus to fix that if they can. The rear spoiler seems loose but that may be the way it is because of the opening rear window. There is a slight blip in the idle when I come to a stop sometimes. I think it might be the A/C cycling but it doesn't pose a problem. One has to remember that the older V8 is smoother than a V6.
Maybe because mine is a late 24 build, the small things were worked out so I would think a 25 model would be the same. I've had 4 previous GX's and all have been super reliable with just needing maintenance.
I really like the GX500 with the increased power and acceleration. I think the reason it rides rougher is that they beefed up the suspension to eliminate the roll or lean with the older GX's. If you had an older GX you know what I mean.
If a problem arises with the engine I am confident that Lexus will address it accordingly. They have to larger a reputation for quality and dependability. My Opinion.