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Discussion Starter · #1 ·
I have a 94 c2500 with the 6.5TD and it will not shift into overdrive until completely up to temp. But if you shut it off for even a second and restart it takes about 5 miles for it to shift into overdrive again. Doesn’t slip or shift hard. Any help is appreciated.
 

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Welcome to DieselPlace
(y)
 
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1995 GMC Suburban
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How is the condition of the fluid? Have you changed it before?
A good trans shop should be able to hook up a computer to diagnose the issue.
 

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You should check for trouble codes. Its simple and free. That will point you in the right direction. You may just have a trans temp sensor or pressure switch going bad. Which will usually set a code.
How to is in here under codes. Info: - The 6.5L FAQ's... The Master List of...
 

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Discussion Starter · #5 ·
You should check for trouble codes. Its simple and free. That will point you in the right direction. You may just have a trans temp sensor or pressure switch going bad. Which will usually set a code.
How to is in here under codes. Info: - The 6.5L FAQ's... The Master List of...
Fluid looks relatively new, I’ve just recently purchased the truck. I’ve ran the codes on it and none of them are trans related.
 

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What codes are coming up?
 

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Engine coolant temp sensor controls overdrive and torque convertor lock up. It is most likely going out. Best to replace with AC Delco.
 
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Discussion Starter · #9 ·
Engine coolant temp sensor controls overdrive and torque convertor lock up. It is most likely going out. Best to replace with AC Delco.
I’ll give it a try tomorrow and post back with results. Thanks for the help!
 

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Does cruise control work?
 

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Discussion Starter · #12 ·
Engine coolant temp sensor controls overdrive and torque convertor lock up. It is most likely going out. Best to replace with AC Delco.
Just wanted to reply back, replaced both coolant temp sensors (one on the head on drivers side, and the one by the cross over tube) and it fixed the issue. Thanks for the advice!
 

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Just wanted to reply back, replaced both coolant temp sensors (one on the head on drivers side, and the one by the cross over tube) and it fixed the issue. Thanks for the advice!
Glad your issue is resolved.
Thanks for giving us an update!
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Great news!
Re the code for the APPS. It is also most likely on the way out. There is good info on it under APP in the 6.5 FAQ.
 
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Like OKd said, thanks for the conclusion. Well done.
 
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