The difference between 4H and 4L is the amount of time for which the transmission is engaged in each gear. 4H is a four-wheel drive system that engages the transmission for a longer duration of time in each gear, while 4L is a four-wheel drive system that engages the transmission for a shorter duration of time in each gear. 4H is used for higher speeds and more power, while 4L is used for lower speeds and more traction.
In 4H, the transmission is engaged longer, so the driver can get more power and acceleration. This is useful for off-road driving and towing. 4L is used in slower speed situations like rock crawling and mud bogging. Since the transmission is engaged for a shorter period of time, the vehicle has more traction and is better able to climb obstacles.