Should I change my Transmission fluid.

When is it too late? I just crossed over 80k on a truck I bought with around 70k. Nothing in carfax about ATF change/flush. I was planning on doing the cooler-line drain, but would feel like an idiot if I broke something that was working fine.

 

You are not close to "Too Late". Too late is probably twice or more than your mileage; and that is just a loose consensus.

It's definitely a good idea to drain and fill with some new fluid.

 

People need to learn the difference between changing the filter and fluid vs flushing. Flushing disturbs the sediment in the pan and reintroduces it into the transmission causing problems. Drain, filter change, and refill is a part of routine maintenance of all automatic transmissions through their service life.

 

Bought truck with 225k. changed my transmission fluid shortly after buying no issues 10k later.