Chris, the best bet would be PM lexwoody as he had done exhaustive mods on his GX, He has done with the following specs, and many have got great reviews on this mod done. And this includes the front, as it is best to do all 4s.
OME Suspension
Front: 886 Coils, N140s
Rear: 897 Coils, N142

And Spring seat for Rear Coils.

Follow this thread and how he has gone abt the mod on the GX. Courtesy Lexwoody. Great work in detail
http://www.toyota120.com/forum/showthread.php?t=4266

 

Thanks mann777. You are right the air ride will be failing little by little and instead of driving myself crazy, i will just replace it all.

 

Can anyone please confirm if they also have this similar prooblem on their 08 or 09 GX ?

 

which coils should i put in back?

 

I have a 2003 GX 470. The ride quality varies. On cold days the car feels very stiff, and going over a bump feels like there is no damper. Warms days it feels a bit better and there is a bit of cushion. We have replaced shocks and sensors, and for now the car is not bouncing up and down when going over a bump like b4. However, the comfort setting and sport setting is not much different. I am not sure what type of sensor was replaced, but it did solve the bouncing. However, the stiffness and poor ride is still there. I also noticed that the car seems to sit high in the mornings. When i switch the car to Hi, it blinks and stays on for a bit and then goes back to Neutral. Is it supposed to go back to "N' at all times, or stay on whatever position i chose whether its H or L constantly?

I am not sure what else can be done to fix the ride issue Is it possible that comfort/sport switch is not working. Did anyone else encounter these issues?

 

Try cycling the rear height full-up and then "normal" in the morning to see if it helps.

If so, I think the general consensus is:
1) you've got a slow leak in your airbag (that's worse in the cold -- makes sense), or
2) your rear height is adjusted below spec, giving you less wiggle room and causing you to come in contact w/your bumpstops more often in the rear.

I think your barking up the wrong tree w/the shocks. As they weaken, they can exacerbate the issue of bouncing off of the bump stops in the rear, but I think #1 and #2 above are the most likely.

 

Or just put it full-up and take off; it will adjust to the normal setting automatically over 20MPH. I do this every day and the ride is great when doing so.

 

I have noticed my truck is real random in ride quality, tired of trying to get it figured out. I am going full ICON

Seth

 

I went with springs intended for the 4runner and runner coil seat in the rear, $100 in parts and my GX rides better than any of the settings with bad air bags

 

What part #'s did you use and where did you purchase this rear spring kit?
Also, does anyone know if 2013 Bilstien TRD or FJ OEM shocks work on our GX's?
Frt Part # 48510-AD061 for TRD and FJ Frt 48510-0W060 / rear 48530-0W040?
I also unplugged my OEM rear shocks with airbags at full height and for now it rides much better, not flat bottom out
Thx