There's a specific procedure for checking trans fluid level. As far as I understand, checking it cold, is not really cold, but rather not fully warmed up. I believe the proper method (if memory serves me correctly) is to drive the car 20-30 minutes (city driving), then when you are stopped, go through all the gears. It would be a good idea to have the brakes applied! After going slowly, and pausing in each gear, wait 2 minutes, and then check the level, with the engine running and the trans in Park.

If you were to immediately check the level again, you would get a different reading, so I think the 2 minutes and moving throught all the gears is very important. It's not the same as checking your oil.

Tom