TOTAL ELECTRICAL SYSTEM SHUTDOWN DUE TO FAILURE/ACTIVATION OF PASSLOCK SECURITY SYSTEM ON 2000 CHEVROLET K2500 CREW CAB (7.4L ENGINE/AUTOMATIC/4X4) WHILE VEHICLE IS BEING OPERATED AT HIGHWAY SPEED. ENGINE CAN NOT BE RESTARTED WITHOUT BRINGING VEHICLE TO COMPLETE STOP AND PLACING SHIFTER IN "PARK". LOSS OF LIFE, SERIOUS INJURY, AND/OR LOSS OF PROPERTY CAN OCCUR DURING PERFORMANCE OF BRINGING VEHICLE TO COMPLETE STOP WITHOUT ENGINE POWER AVAILABLE. INCIDENT OCCURRED TWICE AND WITHOUT WARNING ON 8/29/03 WHILE AT HIGHWAY SPEEDS. DEALER ATTEMPTED REPAIRS ON 8/31/03 WITH GUIDANCE FROM CHEVROLET TECHNICAL ASSISTANCE. SUITABILITY OF REPAIR NOT GUARANTEED BY DEALER. OWNER REQUESTED DEALER TO DISABLE PASSLOCK SYSTEM. DEALER COULD NOT DISABLE SYSTEM AND INFORMED OWNER THAT CHEVROLET CORPORATE WOULD NOT PROVIDE DEALER WITH INFORMATION ON HOW TO SERVICE, REPAIR, OR DISABLE PASSLOCK SYSTEM. DEALER AND CHEVROLET TECHNICAL ASSISTANCE DETERMINED THAT IGNITION SWITCH COULD BE AT FAULT AND CAUSING VOLTAGE CUTOFF TO PASSLOCK, THEREBY ACTIVATING PASSLOCK. DEALER REPLACED IGNITION SWITCH. OWNER TOOK POSSESSION OF VEHICLE AND DROVE 475 MILES AT WHICH POINT COMPLETE ELECTRICAL FAILURE OCCURRED ON 8/1/03 AND AT HIGHWAY SPEED. VEHICLE WAS ABLE TO BE RESTARTED AFTER BRINGING TO COMPLETE STOP, PUTTING TRANSMISSION IN "PARK", AND TIGHTENING BATTERY POSITIVE ELECTRICAL CABLE. APPARENT CAUSE OF PASSLOCK ACTIVATION WAS LOSS OF BATTERY VOLTAGE. ORIGINAL DIAGNOSIS MADE BY DEALER AND CHEVROLET TECHNICAL ASSI