One of two pickup trucks racing at speeds of more than 90 m.p.h. on the San Bernardino Freeway hit a stalled garbage truck, killing the pickup truck driver and causing serious injury to his five passengers, most of whom were teen-agers. Raymond Ayala, 21, of El Monte, the driver of the pickup truck that was not involved in the collision, was booked into jail on suspicion of involuntary manslaughter and held on $12,500 bail, the California Highway Patrol said. The driver of the other pickup truck, a 23-year-old man from West Covina, was killed in the collision. His name was withheld pending notification of relatives. The accident occurred when one pickup driver tried to overtake the other by moving onto the shoulder of the road--where he struck the garbage truck. A CHP spokesman said Ayala was too far ahead to see the accident and assumed that the other driver had exited the freeway.