Checking Transmission fluid level F150

*The engine needs to be running, in park, on a level surface. Use an 19 mm wrench to remove the shorty dipstick under the vehicle*
The proper ATF fluid is Mercon LV for the 2013 F150.

I changed the fluid in mine today. I did a pan drop and fill. Then I unhooked the return line from the trans cooler and had a friend start the engine until I saw fresh red fluid pump out of the cooler. I had my friend shut off the engine and then I added more fluid until the level was perfect. This way the torque converter gets flushed of all the old fluid. Checking the level is definitely a pain in ass having to lay under the vehicle and not burn your hand on the catalytic converter. Then you have to turn off the engine and add the fluid 1/2 quart at a time... (you don't want to overfill it) until the fluid is at the bottom area of the crosshatched fill zone on the dipstick Starting the engine each time you check the level.

I scoured the internet and was unable to find the answer to my question about whether the engine is supposed to running or not. It DOES NEED to be running. I called a transmission shop and the technician confirmed this fact about checking the transmission fluid.