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Old 09-13-2019, 06:35 PM  
Sawstakes
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T7500 gmc with engine problem

I have a t7500 gmc with a cat 3126 and automatic Allison transmission.

It has started shifting bad. Mostly in high gears. Now low gears are an issue. But the weird thing is it tries to shift and the motor bogs down. Iíll put it in neutral while driving and the motor still wonít rev right for a bit. Then it revs fine. I put it in drive again and it starts to bog again.

Does the transmission communicate with the motor to change rpm when shifting?

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Old 09-13-2019, 07:46 PM  
OkDually
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What year is your GMC T7500? Any mods done to the vehicle?

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Old 09-13-2019, 08:13 PM  
Sawstakes
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1999. No mods that I know of.
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1999 t7500 gmc cat 3126
Allison transmission.

Last edited by OkDually; 09-13-2019 at 08:54 PM. Reason: sig
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Old 09-16-2019, 07:11 AM  
ronjhall
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When I had my truck at Allison service. I was told that many problems that appear to be transmission problems are caused by low power from engine.
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Avg mileage over 76k miles 10.3 mpg. Sold it 5/17.
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