Thanks ljayr for pointing out that inertia can't be the root cause since the needle moves in the same direction that I am turning (needle moves right when turning right).
I thought I would provide an update on a few more things that I have tried.
With the engine running, I tried wiggling the wire to the temperature sending unit to determine if there is an electrical problem. I wriggled every portion from the blade connector to the bundle that goes behind the firewall; no change in the temperature reading.
I next tried bleeding the coolant system again with a new radiator cap. I jacked up the left front portion of the car to ensure the coolant bleed screw near the thermostat was at the highest point. I opened the heater valve, cracked the bleed screw, and ran the car for 15 minutes with a steady coolant drip. I then removed the radiator cap, topped off the coolant, and reinstalled the cap. No change in symptoms.
At this point I am stumped. I don't think the engine is running hot since the reading is 175-185 when driving straight, which seems about right.
Kim - 1987 Spider Quadrifoglio (~170K original owner miles)