My '96 S/C 2WD is being a little cranky this week.

Noticed yesterday that it seemed to have a very slight, random misfire at idle. This morning, started it up after a 20min highway drive and it had a check engine light, and would start out in 2nd gear, not wanting to downshift with throttle as normal. Got to work, let it sit for an hour or so, and getting back home it drove perfectly fine (CEL still illuminated).

Get it home, pull the codes, and it has a P0753 "Shift solenoid A electrical." After a quick look online, I saw that a bad ground or the wiring to the throttle position sensor could cause this. Pulled the TPS plug, cleaned it out, cleared the code, and then went for a test drive. It shifted just fine, but the CEL came back. This time, it was a P0171 "System too lean."

Suspicious of a vacuum leak, I smoke tested the vacuum lines under the engine cover and smoke started coming out of the vacuum control module (pic here). I'm not super familiar with how this system works, but I pulled that little module and it has a small hole and filter on top so it seems like maybe it's supposed to work that way?

I guess my question is: does it seem like this modulator is going bad and causing a vacuum leak? If not, is there another direction I should go? With the van running, I tried spraying it with carb cleaner and didn't notice a change in idle. The misfire seems to randomly come on for 20 seconds or so then clear up, coming back cyclically every minute or so.