Shifting Issues after Fresh Install?

2003 CHEVROLET 1500
173,265 MILES • 5.3L • V8 • 2WD • AUTOMATIC
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ANON_TEE
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I have a 2003 Silverado 1500 that I just had a fresh torque converter and transmission installed. Shortly after installation, I began noticing issues with shifting, and it seemed as if the transmission was slipping out of overdrive, but only when letting off the throttle. The problem persisted, and I was informed that the filter needed to be replaced. I did as advised, but I still have to give it a lot of gas in order to get the truck to shift gears. There was also a loud noise coming from underneath the vehicle. Could this be an error with the installation of the torque converter to the flexplate? Loose bolts or even misalignment during install?
Dec 22, 2025 at 8:50 PM
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STRAILER
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Yes, this can be a bad installation of the transmission or torque converter, but I would check the catalytic converter because when they fall apart it can make a rattle sound and cause the engine to have low vacuum which will make the transmission shift the way you have described. With the engine cold use a rubber mallet and tap the exhaust system to see if you can pin point the source of the rattle. Also, lets run the codes to see if any are stored. This can help us see what's going on as well.

https://www.youtube.com/watch?v=b2IJGfImVvw

Let us know how it goes.
Dec 23, 2025 at 10:58 AM