Just wanted to follow up with a quick update in case any one else is as noobish as me...

So, the default PIDs don't work for the A/F sensor, as they are set up for traditional o2 sensors. I looked through the Toyota PIDs and found the correct ones for AF Sensor Voltage. That, however, doesn't really help me diagnose anything because unlike the o2 sensor, the A/F just receives a relatively constant voltage from the ECU.

Either way, the A/F sensor seems fine, and that's why I was reading 0 volts initially. Sooooo much to learn about these scanners!

EDIT: Also, I've installed a new gas cap, and the 3" clamp after the MAF sensor, and the truck is running even better than before. However, I still have the P0441 code. I can see a couple more vac lines under the hood that are questionable so I'll work on replacing those. The lines back by the tank seem to have been replaced / repaired relatively recently (truck was inspected in January before I purchased it).