To correctly check Automatic Transmission Fluid Level:
Make sure the truck is at NORMAL OPERATING TEMPERATURE and RUNNING.
Park on an even grade, and cycle from Park all the way down to Low, and back to park again. Pull the dipstick, wipe it clean and send it back down through the tube. Make sure the clip locks the dipstick in place, then pull it back out. The level should be at the HOT mark.
Thanks for making this clear!