should car be running to check trans. oil

Yes it should and warmed up to normal temp.

Running in park, warmed up.

Well, most vehicles has a "cold" and "hot" marks on the dipstick, so the level can be checked with either temperature while the engine is running. Start the car, shift it through all the gears - leave the selector in every gear for 2-3 seconds, than back to park. The important thing is, the vehicle should be in level and if you need to add fluid make sure it's the CORRECT one. In your case the correct fluid is a Mercon V. (Mercon 5). Zee