I believe my problem has gone away. When examining my gas cap I notice a little bit of gas collecting on a portion of the gas cap. I removed the rubber seal, cleaned it off, cleaned off some dirt on the gas cap, then put the seal back. That seemed to have done the trick. My gas gauge finally reaches FULL...at least after the last 4 fill ups.
I do notice, however, that the gauge goes about 95% full, then slowly inches to 100% full. I think I remember the gauge going 100% full immediately when the car was "new." Also, I still don't hear the suction action when I remove the gas cap. Maybe I just need to replace the rubber seal and/or the entire gas cap. For now, it's works well enough to NOT irritate me. :-)