Here is the scenario/update (for those who haven't read up on my plight).

I replaced the clutch, rear main seal and oil pan on my car. I removed the engine and transmission to do this.

After returning the engine/transmission to the car, it was hard to start.

It would click (the starter/solenoid), and occasionally slowly crank the engine. most times, it wouldn't do anything. Hooked up to a KNOWN working battery, it would repeat these symptoms. If I had my truck running, and jumped the car, it would start. It ran fine, no symptoms or anything. However, once the engine was shut off, it wouldn't re-start.

I've replaced:

neg battery cable.
pos battery cable.
battery
starter
cable to the alternator.

I've cleaned the grounds and checked continuity/resistance. they're fine.

with the new battery, it does the same symptom. so I thought maybe it was the starter, took it to where I bought it but they said it was fine.

disconnecting the starter from the power, and the battery doesn't drop in volts (I didn't check and don't have the capabilities to check amps).

I get 12+ volts at the ignition. I jumped it and it tries to crank and then just clicks (solenoid). I jumped it both directly from the battery and from the plug towards the back of the engine.

I removed the spark plugs from the car to see if it would in turn crank (suspecting maybe there was a compression issue). It would crank, but not very fast. eventually, it would drain the battery and just click the solenoid.

I was able to manually turn the engine, although after trying to turn it with the starter it tends to be REALLY hard to turn. But give it a little time and I'm able to hand crank the engine.

does anyone have any idea what it could be? It seems to be an electrical issue.