error code 42.

A code 42 on a GM vehicle is a bear to diagnose, I know because I used to be a GM Dealership Journeyman. It stands for a loss of Electronic Spark Timing or EST, which can be caused by many things, like the engine dying, a bad crank sensor on the engine a defective ECM ( engine computer ) or more, like a bad ground etc. I would measure the ohms of the crank sensor on the engine. A lab scope inspection would be even better. Then if that is well within spec, run your truck and when it dies, check for switching ( on-off signal with a test light connected to a positive voltage source ) at the negative side of the coil. See if the ground side is switching, this is checking your ignition module. If there is no switching, check for injector pulse, if no pulse and no switching it could be the Crank Sensor even though they ohm check just fine. The last hing to consider is the ECM. here is a site with the proper specs http://bit.ly/mitchell_repair_manuals_online