Does the battery show 12V when cranking?
Are the battery cable connections clean and tight at both ends of the cables including the ground to the block?
What is the voltage on both terminals of the slave soleniod when cranking?
What is the voltage at the starter soleniod when cranking?
Last are you sure the engine is not hydolocked or siezed?
1997 2400 SCR
5.7 Vortec / Bravo 2