Suspension lop sided (4 bag)

[JimT]

Not something I've dealt with before. But, you could try swapping the bags left and right. If the problem follows the bag then it's something with the bag itself, otherwise it's probably some other component.

On a side note, I had a Z spring break on a single axle daycab once. Seemed fine until I had the trailer jacked around a bit, then the broken side would drop so the trailer was hitting the tire. Straightened out and it'd ride normal. Point is, with enough weight on it the airbag wasn't able to compensate for the broke spring. Have you taken a close look at the springs? In my example the spring had cracked directly between the 2 u-bolts and was hard to spot until I went looking for it.