Have you looked at the in cab controls for the bags ???
My 2500 Dodge truck didn't come with a aux overload spring pack. So anything over 1500 lbs and it sag too much.
I tried the Timbrens but being less than 4" long they too short which caused the rear suspension to have a very short compression stroke and a violent rebound which after two trips was unacceptable. The ride when empty was normal as the Timbrens don't touch unloaded.
I switched to SuperSprings. I still have the good stock ride when empty. When loaded the truck rear suspension now has the normal compression stoke and normal rebound. Now the rear doesn't sag.