Alright, posting on behalf of someone else:
2006 Envoy XL
The vehicle has generally sat for a while, being started to make sure the battery doesn't go dead. Recently, the battery had gone dead, it was charged and started and shut off fine. Today, it was reported to the owner that it wasn't starting again. Again, hooked it to the charger, and started it up to bring the battery back up. This time though, the key is stuck in the ignition in the run position. Note again that this vehicle is a "backup" one and therefore hasn't been used as a DD for a while, so some of the expectations such as parts wearing out seem to have less to do with this, potentially.
-Battery obviously good now
-Shifting to reverse, there is a noticeable little dip in power. Also, turning the wheel left and right, there is also a noticeable dip in power. The charging system warning does not illuminate, possibly re-check for good battery connection?
-Crawled under and examined the harness going into the P/N switch, the one with the white plastic on the connector itself and with some odd little blue tether. The thing seems loose. Like not loose as in disengaging the pins, but has a noticeable little wiggle, it seems odd but so does the connector so I was not sure this is normal. All gear selections properly report on the dash.
-This is the ORIGINAL lock cylinder.
-Also, the battery had been disconnected in an attempt to get the vehicle to stop before I arrived. It did not stop the vehicle. My solution for stopping it until a solution could be had was to pull Relay 41, and then disconnect the battery after the engine stopped.
-Pulled and replaced Relay 41 and then tried restarting before pulling the battery, she started up beautifully not even getting one full "crank" sound before firing up.
So, my thoughts would be the solenoid is giving up in some fashion, the cylinder is dying, or the battery perhaps needs checked for proper voltage and connection. I went on-site to the vehicle and did not have any reference materials with me and limited tools, so I didn't dig too deep, especially since it's not my vehicle. There were codes reporting low voltage on Shift Sol. A and B and the TCC, this was expected as of course the battery was dead. However, the codes were hanging again in pending, should I make sure to revisit the battery?
I am also aware of the TSB on the shift boot stopping the lever from getting in the proper position, it didn't feel to be related to that.