RPMs go up, but the mph doesn't?

2018 BUICK ENVISION
94,000 MILES • 4WD • AUTOMATIC
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WOLF8013
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I've noticed this for the past week or so at a cold start, basically after it's been sitting for a while, such as before or after work.

It starts fine, no warning lights on the dash. Shifts into reverse and drive fine. Starts driving normal until about 20mph. Then if feels like nothing is happening. The RPMs go up, but the mph doesn't. Like I'm pushing on the gas pedal but nothing is happening. It feels like it's going to stall, but doesn't. After a few moments it's back to normal and drives fine.
Apr 19, 2026 at 11:57 AM
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STRAILER
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This sounds like an input shaft speed sensor is going out or is not working, also we need to check the fluid level and condition, (burnt or low) lets run the codes to see which ones are stored this video can help.

https://www.youtube.com/watch?v=LBCpCWEFnTg

Here is a guide to help you with instructions for your car as well.

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

Check out the images (below). Please let us know what happens.

Apr 20, 2026 at 9:46 AM