Roll-off truck air bags won't come up to ride height

First thing that comes to mind is you have a leaking airbag.

 

Install a pressure gauge at the level valve air supply port. Upstream will be a pressure regulator likely at an air tank or the air dryer itself, trace the supply line up front. The pressure will likely be low and you will have a plugged or restricted regulator/ device.

Year, make and model may help narrow things down.

 

ADIS dryer most likely. Trace the line to the dryer. Check pressure at the dryer. New dryer will most likely resolve your issues. Regulator plugged inside dryer.

But check first.

 

Get some gauges on it?

Where I come from new doesn’t necessarily mean good.