What is the battery voltage?
What is the battery voltage when you turn the key to engage the starter, and it "clicks"?
What is the voltage AT THE STARTER SOLENOID main power cable, when the key is turned to engage the starter?
Battery terminals CLEAN and SILVER-COLORED? Battery cable ends CLEAN and SILVER-COLORED (unless they're brass, in which case they should be bright brass colored.)
What is the voltage at the engine side of the main ground cable when the key is turned and the starter clicks?
Can the crankshaft be turned by hand? Is the engine locked-up?
Was there a gap between the flexplate and the torque converter before they were bolted together, or is the torque converter bound-up on the trans pump?
Is the starter shimmed properly?