Don't know about trucks. My best car, a Pontiac Bonneville GXP, has an
automatic load lever. A few
seconds after each start-up you can hear the air pump run to "trim" the
level. The car came with an
accessory air package that connects to the compressor pump via a shrade
valve in the trunk..


My diesel Mercedes wagon has a hydraulic levelling system. The car is rated
for a 1000 Lbs load, a true half-ton.

--
Stupendous Man,
Defender of Freedom, Advocate of Liberty