someotherguy
Truly Awesome
If anybody has a '98-up GMT400 (since they were made in certain configurations for the U.S. market through '02 like the 3500HD) that exhibits the symptom of starts and then shuts off almost immediately, the very first suspect on your list is the Passlock antitheft system which began in '98. The security light on your dash should be flashing (if it's not burned out) and you'll probably have codes stored related to the Passlock system.
When it starts going bad you can try all sorts of remedies, some free - doing a security relearn, cheap - "resistor" trick, expensive - "bypass" units.. or the only one that actually works long-term, and that's have a custom tuning service tune that functionaity OUT of your PCM.
Richard
