Speedometer is way off and transmission not shifting good?

1998 CHEVROLET CHEYENNE
90,000 MILES • 4.3L • V6 • 2WD • AUTOMATIC
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ROMMEL1961
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Speedometer was acting crazy jumping around. Transmission wasn't shifting smoothly. I replaced the vehicle speed sensor. The speedometer is smooth, not jumping around. But it is way off. It pegs out over 100 mph and Transmission still isn't shifting right. I heard that if I unplugged the VSS buffer, it may solve it. However, I can't find that buffer. Can you help?
Jul 19, 2025 at 6:25 PM
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STRAILER
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Yep, it sounds like the buffer is going out. Here is a video to help you:

https://www.youtube.com/watch?v=-NHZZGv4sxY

Let us know how it goes.
Jul 20, 2025 at 11:27 AM
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ROMMEL1961
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Thanks. I'll see if it's behind the glove box like in the video and will let you know.
Jul 20, 2025 at 1:18 PM
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ROMMEL1961
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It's not behind the glove box on this model. Can you advise where it's located on 1998 chevy c1500 4.3 vortec Cheyenne?
Jul 21, 2025 at 8:41 AM
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STRAILER
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Okay, I did some checking, and they don't say where it is, I would assume it will be near the instrument cluster. Do you have a replacement part? Here is the VSSA in the wiring diagrams so it does have one. Check out the images (below).
Image (Click to enlarge)
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Jul 21, 2025 at 10:41 AM