Should I flush the transmission fluid or drain and fill for sluggish shifts?

[AddisonL]

I’m trying to decide if I should get the transmission fluid in my 2015 sedan flushed or just do a drain and fill this time. The manual says “lifetime” fluid, but I’m at 90,000 miles and the shifts are starting to feel a bit sluggish, especially when it’s cold.

[Jack10]

I did a drain and fill around 90k on a similar sedan and the shifts got a bit smoother after a week or so, especially when warm. Cold mornings were still a little laggy, but it wasn’t dramatic.

[George11]

A shop suggested a full flush once, but I heard about older transmissions not liking that and maybe washing away helpful varnish. I did the drain and fill only and kept notes on how it behaved.

[Larry_R]

The term lifetime fluid always seemed vague. At 90k I’d treat it as maintenance you can do if you notice roughness, not a guarantee that you’re good forever. If the transmission has never been changed, a change is reasonable.

[Andrew_W]

I’m not sure that’s the root cause—could be sensor or valve body stuff. If you want to try something practical soon, a drained fill is cheaper and you can compare how it behaves, rather than a flush that might unsettled things.