Good news! I successfully replaced the rear derailleur, gave it new cabling, and after riding it today, I got tired of only being able to use my largest and smallest gears. Then I took a look at the rear cassette and decided to replace it.
[ATTACH=CONFIG]2297[/ATTACH][ATTACH=CONFIG]2298[/ATTACH]
Note the 4th gear sporting some shark fins.
[ATTACH=CONFIG]2299[/ATTACH]
Took it in to Performance Bike and they replaced the cassette (it’s shiny and pretty) that had an additional tooth (slightly better for hills).
[ATTACH=CONFIG]2300[/ATTACH]
My new rear derailleur Shimano RD-3400 Sora (GS Medium cage, 9-speed)
[ATTACH=CONFIG]2301[/ATTACH]
My happy bike, ready for more riding.
Lesson learned: I will remember to clean the chain more often now!