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Ok guys and gals I need help. When driving through a bad thunderstorm a couple of days ago in my wife's 2.8L Colorado the rpm's started going up and down with the accelerator pedal held in the same position. Yesterday when driving it the same thing happened with the transmission also shifting improperly. Any ideas what would cause this? Any help would be appreciated. Thanks in advance. :???:
 

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:welcome to C'Fans.
Before getting into troubleshooting, do a reboot. Just like any computers, the Control Modules sometimes pick up a glitch. Disconnect the battery and let it set for at least an hour. The truck may run a little rough the first time it starts up because the settings returned to default, but it should smooth out. If that doesn't clear up the fluctuating RPMs, let us know.
 

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Ok guys and gals I need help. When driving through a bad thunderstorm a couple of days ago in my wife's 2.8L Colorado the rpm's started going up and down with the accelerator pedal held in the same position. Yesterday when driving it the same thing happened with the transmission also shifting improperly. Any ideas what would cause this? Any help would be appreciated. Thanks in advance. :???:
I realize I'm years late here, but commenting anyway to help others. I recently had this same problem on my 05 Canyon Z71. No check engine lights or any clues as to what could be causing it. Symptoms were fluttering RPMs and unusual/delayed/slow shifting. Always shifted smoothly, just at odd times. Most of the time the truck drove fine. I mostly noticed the problem while driving at highway speeds the RPMs would randomly flutter from around 2,300-2,800 or if I floored it the shifting would be slow/delayed. The first thing I tried was a master solenoid rebuild kit and a fluid/filter change. After installing all new solenoids, wire harness, filter and fluid in my 4L60E transmission I still had the exact same problem as before. Totally bummed. After a bit more research and head scratching I tried replacing the transmission output speed sensor. The part was $20 and I changed it out in about 10 minutes. Bam! Fixed. No more weird shifting or fluttering rpms. Hope this helps someone else out there.
 

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Personally I appreciate anytime someone can post their experience to potentially save others time and $$ by posting a solution. Old thread or not, its great information to have documented! for the next guy doing a search on this issue. You provide a proven possible fix that is the easy and cheap. That is always a great place to start for anyone who does not have the expertise or equipment to do a full/thorough diagnosis. Thanks!
 
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