fluid is only one of many factors for shifting quality. it can be valve body or the clutches.

did this problem exist before changing fluid??

have you changed the fluid as required by the owners manual??

Roy

The problem doesn't exist before the fluid change. I started observing it a month after the fluid change, and i didn't do a transmission flush, it was a drain and fill. Though the OEM ATF recommended was Mazda ATF M-V but since i was unable to get it, i had to make do with the coastal multi vehicle Mercon V that states its compatible to the OEM. One thing i observed again, is after a long drive when the transmission is warmed up much, the shift will be a little smooth all through that day until the next morning when it will be rough again at start of the day.

ok, the mixing of fluid may be [art of it.

i would have all the fluid removed from the trans and have the correct fluid installed. make sure the converter is completely drained.

start there. it may take a little time for results as the fluid will have to penetrate the clutches.

Roy

Could you recommend a best compatible aftermarket ATF for my mazda 6 because from other forums online, there are complaints that coastal ATF is not too good as it has low cold viscosity performance.

i would get the fluid directly from the dealer. dont play around with the aftermarkets.

an opinion from a trans shop may help too. they rebuild them all the time. find out what fluid they use.

Roy

Thanks so much Roy. You just relieved me from this transmission issue frustration. And I have just learnt this from you; "never mix transmission fluids in your car trans". Thanks man, i shall keep you update on how far i have gone with it. Expecting best compatible ATF recommendations from you, please.

Car Details:
2007 Mazda 6i 2.3L (4cylinder)

Cheers!
Ken