PCM corrupted / damaged out of the blue?

My vehicle (LS1B PCM) is licensed and tuned, new battery in good condition. I went to routinely read/write it for like the 100th time lol and it says "FAILED TO UNLOCK". I am not sure what gives, tries most of the common sense basic things and still.
When I go to read it acts as it has a custom lock by another tuner (impossible) and when I go to cal. or full flashed it says not licensed (impossible).
All of this happened on it's own, and if it helps at all I recently ran my 4 year old battery dead by having the key on / engine off to test and replace a blown instrument cluster fuse. I installed a brand new good and proper battery and the car runs great except... for some possibly unrelated reason it now idles slightly and intermittently high. Meaning the "dashpot" (?) it likes to sit at 1100 RPM for no reason until it settles.
What happened to my PCM communication with tuning device and what to do please?
Greatly appreciate in advance you time/attention/clues/help/suggestions!
Don't want to buy another module until I am sure and I understand the cause. Money is tight and an accurate diagnosis is essential. But I am only halfway done tuning this piggy :(
Vehicle is 2001 Z28 manual / stock LS1 - bolt ons if it helps

Update:

Disconnected the negative battery terminal
Disconnected the positive battery terminal
Waited 10 minutes
Disconnected both PCM connectors
No sign of corrosion or other obvious problems
Sprayed liberally with electrical contact cleaning spray
Brushed lightly with soft toothbrush
Dried and coated liberally with dielectric grease
Reconnected everything carefully and properly

Car starts and runs great, check engine light comes on with all the other warning lights when it should - KOEO

Same problem - can't tune or read

Is my PCM possibly hopeless or should I check "No Communication With DLC" type diag. (does anyone have flowchart / schematic)

The thing is it identifies itself, says all connections are good and tells me the vin. Just the UNLOCK fails.

It is (falsely) behaving like a locked and unlicensed module

:( pwease halp

I haven't heard of an LS1 PCM corrupting itself, the LB7 Duramax ECM definitely has a habit of doing that.
Can you just try to read the ECM using V8 and then send support the trace file (or post it up here), that way we can see what the PCM is sending back.