From what I've seen, about the only thing to make fluid upchuck out the filler pipe is heat and possibly combined with too much fluid to start with. It's not a regular situation at all.
Changing the fluid, if it hasn't been changed in a while, is always a good move plus when you remove the pan, you'll see how much deposits are there of friction material and/or metal. Some is normal, but what is too much takes a practiced eye. If the filter's clogged, it will most likely decrease all of the pressures, resulting in slippage, late or delayed upshifts and engagement, and other things. Slippage causes heat and heat causes upchuck in extreme cases. Upchuck can even cause localized underhood fires!
There is a case vent in the top side of the transmission. It's purpose is not specifically for extra fluid to escape from, though. By nature, it's higher on the trans than the fluid entry into the filler pipe.
In checking the fluid level, the vehicle needs to be at operating temperature and have been driven about 10 miles or so so that ALL fluids are up to their stabilized temperature, plus on level ground. Then follow the instructions in the Chrysler service manual of putting your foot on the brake and slowly moving the gear shift through all shift positions and end up in Neutral or Park as specified in the manual or on the dipstick itself (I believe it is Neutral) with the parking brake fully applied (might have to have a helper use the foot brake or deactivate the automatic parking brake release by removing and temporarily plugging the vacuum hose to the vacuum actuator). Then check the fluid by first wiping off the dipstick and reinserting it into the filler tube for a moment. Then carefully withdraw it and see where the fluid level is. Ideally, it should be in the area between "Full" and "Add". It does not hurt for it to be closer to the "Add" line
when at operating temperature as that can have a little tolerance for more heavy duty driving in the mix. Key thing is that it is not above the "Full" mark (although just a hair might be ok). There is only about a pint between "Add" and "Full". If there are any marks below "Add", those are there for references of cold weather (as 0 degrees or so).
As the transmission cooler is in the bottom of the radiator, a partially clogged radiator could be an issue too. What many times looks good on the top side can be really bad on the bottom of the tubes, even if it "looks" like good flow on the top side. Might even some hoses having internal problems too.
For now, just a basic fluid & filter change and some quality atf might be the best course to initially diagnose the situation. I might take about 4 quarts to start with in the refill from a fluid change. Then, with the temperature in the "normal" range, add fluid a little at a time until the specified amount is installed (probably in the range of 5 quarts total?).
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