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Q: My truck selectively shifts hard

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My truck has started to shift harder. Only when taking off. For example at a red light not shifting into first when starting but while I start to accelerate. Also hits harder when I come to a stop. Not going into park but coming to a stop at a red light. It seems to turn over harder than normal. I checked the transmission fluid levels looked a little high, I was told by one place a long time ago I should change fluid but never from any other place more recently. I just replaced the alternator and have a new pully system in place. Is there any cause for this? Hopefully not a failing transmission.

My car has 111670 miles.
My car has an automatic transmission.

The first task is to get the transmission fluid to the proper level. Overfilling the transmission can cause "foaming" of the fluid, with any excess being forced out at the dipstick or any weak seals, which can get messy. It can cause abnormal shift behavior as well. It is possible there is a hydraulic pressure problem internally causing high fluid pressure to shift mechanisms (clutches and bands) within the transmission. I would recommend you have a reputable technician, such as one from YourMechanic, perform a diagnostic service on your transmission to lower the fluid level and determine the source of your hard shifting.

As to whether or not you should change the fluid, you are correct, some mechanics say to never change the transmission fluid while some say to change it every 75-100K miles. The discussion has to do with the perceived benefits of fresh additives in the new fluid and a clean filter "helping" some components of the transmission (e.g., the seals, shift solenoids, valve body), versus the potential negative effects of fresh fluid stirring up worn clutch material in the pan or getting on clutch friction surfaces in the transmission. This is a "religious" battle - there’s no right or wrong answer. I keep my cars a long time, and change the fluid and filter every 75K miles.

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