To the best of my knowledge the transmission fluid level is checked with the engine running and the transmission in Park. If you change the fluid you typically add all but the last pint or so then start the engine and shift the transmission from Park through the various gears several times. Recheck the 'cold' level and add fluid, as required. Then drive the car to bring the transmission up to temperature and check the 'hot' level. Add fluid, as required to bring it to the full 'hot' level being very careful not to overfill.

__________________
Fred Hoelzle