An 18-year-old Lakeside man died Sunday after he lost control of his pickup truck while chasing another vehicle at a high speed, the California Highway Patrol reported. Shawnee L. Flint was pursuing a vehicle eastbound on Lakeshore Drive just west of Petite Lane when his 1975 Chevrolet truck struck a street sign, fire hydrant, fence, parked car and mailbox, and then overturned, the CHP said. Flint was pinned inside the vehicle before being transported by Life Flight to Sharp Memorial Hospital, where he died at 2:15 a.m. There were two passengers in Flint's truck at the time of the crash. Shannon Wilkey, 17, was treated for moderate injuries at Grossmont Hospital; Randy Salewski, 17, was not hurt.