Transmission issue or speed sensor issue?

2008 CHEVROLET SILVERADO
175,000 MILES • 6.0L • V8 • 4WD • AUTOMATIC
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NIKI BARNES
The truck had been driving fine until a radiator hose blew a couple weeks ago. We replaced the radiator (it had a very slow leak) and hoses. I drove it to work 2 days later and, on the way home, I stopped at a light and when I went to go it wouldn't shift out of first gear, RPMs would go to around 3,000 and the speedometer needle was bouncing. We replaced the speed sensor after that. I drove it to work again the next day and half way to work I stopped at a light, and it down shifted really rough as I was coming to a stop. When the light turned green, I accelerated and same thing as before, it wouldn't shift out of first gear and the speedometer needle was bouncing. I limped it in to work and upon further inspection the dipstick tube for the transmission has broken off. presumably from the hose blowing the week before. We called a transmission shop, and they said they didn't even need to look at it, it needs a new transmission $5,000. So, my truck is still sitting at work and I'm skeptical.

Could it be that the speed sensor is faulty again? If so, what could be causing it to happen so fast after just replacing it? Or is it really that the transmission needs to be replaced?
Feb 9, 2025 at 2:55 PM
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STRAILER
  • ASE Certified Mechanic
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  • ASE Certified Mechanic
So to be clear the sensors you replaced were inside the transmission? Here are the locations of the sensors so you can confirm, also let's run the codes to see if any are stored.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If the transmission is bad most of the time the fluid will smell burnt, can you please confirm this as well? Check out the images (below). Please upload pictures or videos in your response of any problems so we can see what to help you with.
Feb 10, 2025 at 10:47 AM
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