No spark

The place to start would have been by reading and recording the diagnostic fault codes, but disconnecting the engine computer erased them, so that valuable information was lost. Replacing random parts is not a cost-effective way to diagnose this problem. You were right that the crankshaft position sensor can cause a crank/no-start problem. (By the way, "cranking" means the starter spins the engine, and yours is). You overlooked the camshaft position sensor. On some GM V-6 engines, with a failed camshaft position sensor, you have a thirty three percent chance the engine will start and run when the computer randomly picks which pair of cylinders to fire first. On other engines there will be no spark and no injector pulses.

Diagnostic fault codes for these two sensors often do not set just from cranking the engine. They may only set while a stalled engine is coasting to a stop. To find if a signal is missing from one of them, you need a scanner to view live data. That will list the sensors with an indication to show if they are working.

I think the fastest way to pursue this is to see if you can borrow a scanner from an auto parts store that rents or borrows tools, or tow the car to a shop where they can connect their scanner and see if the two signals are showing up at the Engine Computer. You're going into this blind, like trying to stumble through a forest while wearing a blindfold. The fastest way out of the forest is to figure out how to get the blindfold off.

If you're going to do more of this type of repair in the future, consider buying your own scanner. If you look on eBay, there's a lot of dealer-level stuff, and some are at real good prices. I don't promote Snapon, but if you look at their "Solus Edge", these lose their value very quickly due to the extremely high cost of annual updates. These sell new for less than $4000.00, but the updates cost $1000.00 per year. You can't skip any years. To make current a unit updated to 2014, you have to buy the 2015 and 2016 updates before you can buy the 2017 update. That customer-unfriendly business practice is why I don't buy Snapon products, but for what you're working on, it can be a good value and save the cost of a couple of trips to the repair shop. You can find these updated to only 2012 to 2014 for less than $800.00. They won't bring much more because it will cost more to update them to current levels than it costs to buy a new one.