The trasmission fluid level is measured after car sits overnight. Now, I did feel the transmission hard shift at ~ 40 MPH. Anything I need to do?
IMO, before you do anything, we need to determine if you've properly checked the tranny fluid level.
If you've been checking it with the engine off & the tranny fluid cold, after an overnight sit like you'd check the engines oil level, then you've not done it right.
Your owners manual will specify how to do it.
If you don't have a owners manual, try the followng.
Don't know where you are right now, nor how cold it is, but to Fully warm the transmission fluid before checking, it might reqire a 10-20 mile drive, to bring it up to full operating temperature & this is very important in order that you get an accurate dipstick reading.
After warming it up & stopping on a level surface, as has been suggested, set the parking brake, so the vehicle won't move & with the tranny fluid warmed to oerating temp & the engine running at warm idle, slowly shift into ALL gears, so you feel each one engage, including Reverse, then end in "P".
Leave the engne idling in "Park", raise the hood, pull & wipe the tranny dipstick, reinsert it fully, wait say 5 seconds, then pull & read the dipstick fluid level.
Done thusly, the level shouldn't be above the cross hatched area on the dipstick.
If it's overfilled, you can easily pump some out, as I outlined above.
Once you know the tranny fluid level is right, let us know how it's color looks, smells & feels & how the tranny shifting is behaving.