Was able to drive the truck yesterday. When I got in and fiddled with things, I was able to pull harder than should be necessary (pretty damned hard) to get the vehicle out of park and it came out. The truck was parked facing downhill, and I wonder if this contributed to the reluctance of the transmission to leave park. Going to test this out.
I also thought, given this shifting difficulty, perhaps the transmission had a fluid issue (never changed, dry, etc.). Drained the fluid and replaced. What came out looked fresh/clean so I think she is good. Going to change the transmission filter (no record of it ever being done) and fluid once more mid-week.