Well, that was one problem fixed!
Found the rouge hose and where it's supposed to go on the DPFE sensor.
Also changed the IAC valve and replaced an EGR bolt I lost while doing the UIM/LIM cleaning. Also found the #11 20A fuse blown in the engine fuse box. Dunno what sort of wierd stuff caused that to blow, but yeah...
After about 1 minute of running, the CEL came back on (I had the battery disconnected for like 30 minutes).
Doesn't stall now, but still revs to like 2500RPM and holds for an idle, then drops, then goes back up.
Seems like a big vacuum leak, gonna get some carb cleaner and spray it around since my visual inspection hasn't found any problems.