Trans fluid pressure- help!

2006 Prius with 130k miles. Bought at around 115k and it had been serviced at a dealer with new brakes, oil change and ???

I decided to change the trans fluid now that it has 130k since I was unsure how old it was. The car was about as level as can be expected so I jacked it up in front to loosen the fill so I could slowly lower the jack to find out what the starting level was as added precaution. As soon as I broke the fill bolt loose I could hear air escaping and as I loosened it more the fluid shot out. I got about 1 cup in the catch pan and lowered the jack to level the car and ended up with 2 cups. Initial thoughts are it was roughly 2 cups over filled. Has anyone ran into this pressure situation and is it normal or could it have built pressure due to being too full?
Secondly the fluid looks as red and clean as the new fluid so I am inclined to just tighten the fill cap and wait another 15k miles.

Thoughts?

 

Thanks everyone for input so far. I think I duplicated a thread, as I was getting "server errors" when I attempted to post. Hopefully the mods can delete the other one.

To answer some comments, I started with the car on a level surface and only raised the front above level to get a reference for how much was in it as I slowly lowered it. In the end I lowered it the entire way to level or just above (definitely wasn't low), and let fluid drain out the fill. Final outcome (measured) was 2 cup extracted.

Based on feedback I feel confident torquing the fill plug and waiting another 15k although I will check the thread about the vent and see where that leads.

Oh, and car was not operated 13 hours before messing with the fluid so it was cold. And that fluid stinks! I had to smell the new fluid just to make sure the correct stuff was in the trans.

The vehicle appeared to be dealer serviced so odd it was over filled. I assume it had to be raised fairly high in front to stuff in the extra 2 cups. OR my front struts are sagging from the time fluid was changed.. but it drives fine.

 

Drain is in the front and the new fluid stinks just like the old. I have worked on autos my entire life, so I have smelled all kinds of fluids but the smell of this fluid is unique.

 

Just put a level on the concrete pad for a sanity check and it was level. I knew that because I poured the pad but wanted to ensure it didn't settle or something.

 

I just thought of something.. What I thought was pressure may have been vacuum. That might make sense why the oil wasn't being forced out while I was unscrewing the plug. Had it been pressure it should have started leaking out past the threads being over filled but it didnt rush out until I pulled the plug completely.

This kind of came to me while reading on the internet that these transmissions will form a vacuum when they cool.