05 GT - Overfilled 5-speed transmission?

Does anyone know how much fluid the manual transmission in an '05 GT would hold if it were filled all the way up to the fill hole?

The reason I ask is because I'm changing transmission fluid right now. A quick google search told me that when full the fluid level should be ~1/2" below the fill hole and the transmission should take around 3.25 quarts... ok, no problem. Edit to note: the car is just about level - I jacked the front and rear up evenly. A bubble level on the frame rail shows that the rear end is just a hair higher than the front but not by much.

Well I put right around 3 quarts, maybe a bit more, and measured the fluid at just about a half inch below the fill hole. I figured there must be a bit of oil left in the transmission somewhere so it's not taking the full 3.25. Still no problem.

Then I poured my old oil from the oil pan into a 1-gallon jug... and the 1-gallon jug is full. It seems like 4 quarts of transmission fluid came out of my transmission.

I'm curious wtf is up with that. Will the transmission take 4 quarts if it's filled all the way up to the fill hole? Maybe the previous owner replaced the fluid at some point and they (or a shop) filled the trans all the way up to the fill hole? Any ideas?