08 Trans shfits hard some-times when engine at operating Temp

Weird When I start out in the morning the transmission shifts nice and smooth once the engine reaches operating temperature the transmission shifts hard. When I shift manually it works ok. There are no codes on the dash. I did drain the trany at the pan (did not remove) the fluid was dark but no metal or other fragments. I may have made a mistake by adding 3-quarts of Mercon V fluid. This did soften the shift a bit. I was thinking of picking-up 3 quarts of MV fluid from the mazada dealer and giving that a try hopefully it will soften the shifts a bit more and if it does, I will change the fluid again. Any thoughts on my actions or is it wishful thinking on my part.

I can not share any history on the car I bought it a few days ago and of course when I test drove the car the engine was cold and all was good during the test drive.

do a complete trans fluid flush.
Many owners don't know you change the fluid every 30k I think its 30.
I change the fluid in the pan every 3k with my oil change. I have over 180k on my 08.

I posted links to some of the recent threads that might be worth the read. They have URL's to other related material also. For transmissions calling for M5 fluid, you will be in pretty good shape if you choose M5 fluid from the Mazda dealer or FNR5 from the Ford dealer (Motorcraft brand). There are some good aftermarket choices for ATF as well but per Mazda, straight Mercon and Mercon V should not to be used in transmissions calling for M5 ATF. Hopefully fresh correct ATF will resolve the problem.

http://www.mazdas247.com/forum/show...-ATF-at-35k-it-s-gray-at-42k-(2013-Mazda5-GT)
http://www.mazdas247.com/forum/showthread.php?123855559-Trans-fluid-change