Well, after flashing the stock KitKat ODIN twice, and no WiFi, I decided to go back to Jelly 4.3, since everything was working there. Unfortunately, flashing the KiKat odin image replaces the bootloader, so technically speaking there's no going back, and I knew that. Since I had nothing to lose, I went ahead with it. As expected, Jelly did not boot, it got stuck at the T-Mo logo animation. After about 10 minutes of looking at the logo, I pulled the battery. Then, for sh..ts a giggles, I decided to reflash the KitKat for the 3rd time, and voila, WiFi started working.
I don't know if trying to flash Jelly had anything to do with it, or if it was a coincidence, and the 3rd time flashing KitKat was the charm, but that's how I got it working for me.