Engine won't crank. Pass-lock? Anti-theft

Computer problem
1998 GMC Yukon V8 Four Wheel Drive Automatic 180k miles

'98 Yukon SLT. Battery died, charged it up. Now it won't crank at all. The interior lights flash. The red LED below the gauge cluster flashes 5 times repeatedly. It does this for a minute or two, then stops flashing the interior lights. The LED remains flashing 5 times, then off a few seconds, then 5 times again.

I've read around, but am confused. Is this the pass-lock? I'm not sure because it won't even crank. The pass lock seems to let it start, but cuts off fuel so it stalls. The truck won't start in the first place.

Is this some other anti-theft system? How do I reset it? I tried the "turn on, let sit 15 minutes, turn off, then start". I tried that 3 times with no luck. I used a "spare key", however. Do I need the key with the black rubbery head? What is the exact procedure? I see variances: 10 minutes, 15 minutes; try 3 times, try to crank, don't try to crank; doors open, doors closed; etc.

I was hoping it was just something that needed to be reset or that I needed to use the "regular" key instead of a spare. Any idea how much that module might cost to replace?

Thank you in advance for your responses.