I have a 2000 Mazda Protege 1.8L with 145k and have a few questions about changing the transmission fluid.

I've been told that you do not want to flush and/or change the transmission fluid on higher mileage vehicles because it can create more problems. My transmission isn't as smooth as I would like it to be and I'm wondering what my options are. Can I just drain and replace the fluid with less risk instead of flushing? Do any of the transmission additives on the market work?

Any input is appreciated. Thanks.

 

Drain it. Fill it. Drive for 100kms/mls. Repeat & check.

 

Follow the man with the scythe.

There was a period when old tranny fluid created a layer of varnish on the inside walls of transmission. When the fluid was flushed the detergents in the new fluid loosened the varnish in big pieces wich clogged the filter and passages leading to tranny failure. However the fluids have been improved so much that varnish build up is no longer common.
That's why grim_reaper is spot on with his recommendation. You will see what comes off after a good ride and your tranny will still be alive.