So, CEL comes on, P0446 code, Evaporative Emission Vent System Performance
Evap. Vent Solenoid - Removed it (a pain, but very doable...it's located in a poor place for access; GM relocated it on later models) and checked it for function w/12V plus blowing thru it. Was OK.

Evap. Purge Solenoid - Not sure if this component would even cause a P0446, but took it off (easy) and checked its function w/12V plus blowing thru it to see if it actually opens/closes. Was OK.

Evap. Canister. - Removed it (easy) and could not determine if enough air was able to move thru it. Also, it dripped some gas and felt very hard and bulgy on one end. Sawed off the bottom (carefully at seam) to find it was in great shape inside. Put it back together w/JB Weld.

Next was the Gas Tank Pressure Sensor. I knew this component was really a prime suspect, but did not think I could get to it and did not have a way to check the signal voltage coming from it (without paying a garage to do it). Finally, just reached up on top of the tank on the driver's side near where the fill hose enters and disconnected the tank sensor plug. Cable was long enough to allow me to meter the 3 plug pins. Found that 5V and ground were present with key on, so back plugged a small nail into the 3rd (middle) pin, attached to my voltmeter, and re-plugged. With key on, it read 0.23V using tank ground strap for ground. I knew (from 'net) that it should be around 1.5V. Ordered a new Ebay sensor ($24.49) and when it came, used flat bladed brake adj. tool to pry up the old sensor (after blowing off the top of the tank w/compressed air) and installed the new. I also plugged a long wire into the back of the middle pin so in the future the voltage can be read without having to remove the sensor. No more codes so far. Hope this helps someone.

Gerald