A quick little update for you guys.
I haven't been able to identify the ground for the O2 and the MAP sensors. Today, I noticed that the vacuum line from the TBI to the EGR valve was disconnected on the EGR side. I reconnected it, started the truck, and she ran fine, albeit idling a bit low. No SES codes after idling for roughly two minutes, so I shut it down. About 30 minutes, I left to pick my brother up from the shop as he was getting his car inspected. As soon as I started the truck up, the SES light came on, but I noticed no abnormal running. Unlike the previous SES light, this one stayed on the entire time I was driving. As I was leaving the parking lot of the shop, the trucked started running very rough. It felt like it was misfiring and it stalled twice in the parking lot. One of the mechanics in the lot gave me a sympathetic thumbs up as I passed by him. I managed to limp out onto the street, where conditions greatly improved. Once I started driving, there were no signs of a misfire, although I could smell the unburnt fuel. At stoplights, it ran rough and idled low, although it didn't come close to stalling like it did at the shop.
After returning home, I pulled the codes. Codes were 13, 33, 35, and 45. 34 dropped off and 33 and 35 were added. It seems wrong to me that the vacuum would be registering as high with the EGR valve disconnected (for the sake of conversation, I'm assuming the EGR was disconnected when the previous light was set) and low once the EGR was connected - doesn't 33 indicate a leak?
The second code, 35, indicates an IAC fault. I'm not convinced that the IAC is actually at fault, as the code didn't appear until I connected the EGR line. But I also can't see a relation between the IAC and the EGR. Any ideas as to what my next steps should be?