Marlene does this same thing sometimes...

If she looks like she's squatting I walk back, hop on the bumper and work the suspension a little. She'll pump right up.

My theory is this: after a zillion miles of the level sensing valve arm pretty much sitting in the same place, the valve's actuating arm resists moving outside of its normal range of travel. When the suspension is pushed down with a load, it simply deflects the transverse rod in the suspension instead of moving the valve arm and correctly sensing the ride height.

Someday, I'll get around to changing out the fluid. At that time I may pull that valve apart and see if there is anything obviously wrong and if cleaning helps any.

As the accumulators age, the suspension will settle too. Recently, I've had to adjust the height of the rear end.

I have the height spec at home...I'll post it here when I can.

__________________
Never a dull moment at Berry Hill Farm.