A couple of months ago, I was driving through town with the A/C on. At a stoplight, I saw smoke coming out from under the car. I pulled over, and the transmission was puking fluid out. I'm pretty sure it's from the fent hole. I figured the transmission was gone, so I got it to a parking lot and got a ride home. I later came back and filled it with fluid (about 2 quarts), and drove it to a transmission shop. Well, nothing happened, no slipping or leaking or anything. The shop came to the conclusion that it just got hot. So I drove it around for a couple more weeks with no problems, until one day when I was using A/C, and it did the same thing again. I filled it back up, and since then I haven't used the A/C, and have had no problems. Is it possible that running the A/C can affect the transmission? If I turn the A/C on, when I'm at idle, there's an intermittant slight rumble, and the rpms drop, then go back up. This is in a 93 P71 with and AODE, btw.

Have you checked for fault codes, specifically fault code 539, possibly others?
Otherwise you may have a cooling system prob, leaves in front of rad, bent fins on rad or condensor, plugged rad core, bad fan clutch etc.

Weird. Don't know what to tell you.

I would check for debris between the ac condenser and the radiator. I had a large amount of debris packed in between there, mostly tree cotton and such.
I wasn't having any issues besides a 3/4 hot reading on the temp gauge with the ac on. I pulled the fan shroud and rinsed out the area. That was 4 years ago, no problems since.
The problem was caused by a misaligned air-dam on the drivers side bottom of the radiator support. The air-dam is meant to guide air from the bumper openings through the condenser to the radiator. Mine was allowing air to be pulled in from between the condenser and radiator. Snapped it back into place and all has been well.

Air dams. Haven't heard much mentioned on those. I trimmed mine to look better as they were hanging and I removed the narrow plastic strip that runs along the bottom of the radiator. I know it is to guide air up into the right place but it was twisted and crunched so bad that i took it off. No problem with that being off so far. I don't advise to take it off but works ok for me-so far. All the C.H.P. cars have bent twisted up airdeflectors under that spot-everyone of them. I even trimmed the splash guards above the suspension near the wheelwells on both sides to prevent any binding of those rubber flaps when making turns. Just so I don't splash through any big puddles. I already did however and no water got onto the exhaust manifold so ? You say you think it leaked through the vent hole and you added another 2 quarts? If it were overfull then something is not adding up or? You have a bigger problem I think but don't overfill it. What was the reading on the stick before and after the leak and overheating? Something may be plugged intermittently or? Never hurts to wash out the radiators and the outside of them also but I suspect you may need a new tranny-Hope not but ? Did it just start doing that? How long have you had the car? More info. Correct fluid in there? I don't think your AC is the problem. Does your fan and belt work ok?