Automatic Transmission Fluid Change - Australia

Can you be a little more specific as to "hard gear shifting".Hard as in prolonged or hard as in abrupt.
Like christofphera said Dexron is ok to use and is identical to Mercon which is not made any more.
CAUTION:You have to follow the exact procedure for the oil change in order to end up with a complete change and not a partial one.

Well techy, the symptoms you report point to worn clutch disks.
The disks are slipping due to the loss of pressure and that is why there is a delay in gears change.
It is something that can be fixed by an auto tranny mechanic at a much lower cost from getting a new or reconditioned transmission.
These clutch disks can be found at the dealer.They are ridiculously cheap but it is the labour hours that might cost you around $1500.
I had this done on my car at 85000km because of the excess punishment the transmission was getting with my rally-raids.
As I have mentioned before, you may want to try the LUCAS ransmission conditioner.It really does the job it says it does and may prolong major service.

Christophera's 170000km with that transmission is quite an achievement.

PS:You probably have noticed that the symptoms you mentioned are not as evident when you first drive after a night's rest but they show up after a few minutes when the transmission has warmed up.

Well, it actually has a filter which is internal and you cannot change it at every oil change but only after dissasseblying the transmission.