I was trying to rule out "foaming" (which occurs while running) due to overfill. Trans fluid should be only a couple inches above the full mark when checked not running. If you check after sitting for awhile, there is no reason for the fluid to be "halfway up the stick".

 

Then again when in doubt dump it out. Transmission expensive.... Fluid a whole lot cheaper. I'd just redo the fluid if your super worried.
Also, I agree with others about the radiator contamination. Best to check it.