1998 Chevrolet C3500 dies randomly when driving down the road - uphill, downhill or flat surfaces. Typically doesn't happen when it's cold. Sometimes it starts back up and sometimes it doesn't. When the engine dies, the Security,brake,anti-lock and service engine lights all come on. Sometimes you hear a clicking under the dash. A new ignition switch was just installed and diagnostics done with no results???

SOURCE: anti lock brakes activation

if abs activates when it should not,,, it means abs module senses one or more wheel sensores under 3 mph and the other sensores are above 3 mph. .the cause of this is usualy a bad wheel speed sensor or excessive air gap between the sensor and ringwheel. you need an abs data scanner to hook up and go for a test drive to find out which sensor is the culprit.

SOURCE: Blazer Stalling, Please Help

I am not sure but you might want to check the pressure of the fuel pump.

SOURCE: 96 s10 shuts off dash lights blink and truck dies for seveal minu

check the alternator

SOURCE: A friend has a 1989 Chevy Suburban with two

If it has injectors it has a ecu, if it has an ecu it has a diagnostic port (normally under the drivers/passenger dash) if you look down at seat botton level you should see a small black port) You can go to any auto zone or parts place and they will scan it for free. You may have a head gasket issue with overheating or your cooling fan(s) may not be turning on. Check the codes first

SOURCE: Anti-lock brakes engaging when not needed

sounds like you have a wheel speed sensor going out.. need to have it scanned to see which one is dropping out and making abs kick in..