someone correct me if I'm wrong here, but if you drain some of your coolant into a clear container and also some of your tranny fluid into a different container you should be able to let it sit for a few hours and see if it settles out in different levels (an oil and a water level). but your tranny fluid being overfull is a pretty clear signal in my opinion.
Make sure you drain it after its been run long enough for the thermostat to open and the transmission fluid to circulate, otherwise you're just collecting whatever is in the sump and it likely won't separate.