Basic 4WD. The front axles can bang too.
4H or 4L are not for road use. Pretty sure the front-to-rear differential locks up and since the wheels all have different rotational speeds due to turns, etc the axles will wind up like torsion springs until the the road wheels slip/break loose, and move probably a fraction of an inch with a loud bang or series of bangs. If on a loose surface this won't happen as the slippage is constant and torsion never builds up. This happens with all conventional 4WD systems.
4Auto is used for the purpose you describe on the road. Front axle engages as required which is rarely. Works well off road. You can run in 4Auto all the time if you want but it puts unnecessary wear on the system. Use 2H unless you need all four wheels -- this ain't a Subaru with all wheel drive.
Find yourself a quiet street and be in 2H. Without changing the throttle switch to 4Auto and you'll feel the truck slow a tiny bit due to the added parts, friction, and wear you just added to the system.
-- Chuck
