Leveling valve

That's where I was going. Looking for all sorts of info on coals particular problem. I'm not an o/o but I've never had a leveling vavle replaced on the company trucks.

Process of elimination

 

Could it be slipping out of adjustment? Not sure what your rod looks like, but....?

 

Did you inspect the old vavles for clues? Looking for foreign matter in them?

 

I dump mine every time I drop my trailer also. I don't think that would do it, perhaps if the suspension leaked down every time the truck shut off (but I know you take better care of equipment then that)

 

Mine leaks a tiny bit too. I've been meaning to change it for years but, something else always takes priority.

 

The only truck I ever bought new, I ordered with 2 leveling valves (one for each side) That was a pain. I took one off before the truck was 6 months old

 

I have to replace mine about once a year because it starts failing to keep the truck at a consistent ride height, it will vary as much as an inch sometimes.

 

Check air bags with soapy water. as they are lifting up truck.