Question about 2001 GMC Sierra 2500HD

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01 GMC 2500HD 8.1 wont downshift while trying to accelerate

Recently my 01 2500HD sometimes wont downshift when i step on the gas hard it feels like it is hitting the govenor . I can shut off the truck for a bit and drive off and hammer on it and it will scream, shifting perfectly all the way to a 100mph . It is four wheel drive with an 8.1liter engine and 5spd allison transmission . I think it would be an electical problem and i would like to know exactly what the cause is and how to fix it. I love this truck and i do all the oil and fliud changes at or before their time. can someone please help me with my problem ?

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Check with dealer i had the same truck and as i remember there was a recall on them having to do with the shift indicator or something

Posted on Feb 06, 2009

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I have a 01 also same set-up as yours. I had some problems with not shifting into 3rd or dropping out of 3rd/over drive down to 1st while driving (not fun). Then all all kinds of check engine, brake, and ABS warning lights would come on. Took it to the dealer they cleaned a connector and it was fine for a while. Then happen again. I found the connector in question by the transmission and something a lot brake lines go into. Poke around under the driver side door you find it (there are 2 one looks like a power connector and one for the computer and control stuff). I cleaned it and fixed the problem, but would come back. I got some of that electrical grease stuff smeared it on the contacts, I haven't had the problem since bin about 3 years now. I assuming the connector has signals for the brake system and trans going thought it. Though this may not be your a problem there are a bunch of connectors going the tran that may need to reseated or cleaned.

The truck was under warranty at the time, but they still write up a invoice. The price stated was $160, it might be worth you time to check the wiring.

Posted on Mar 04, 2010

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There is a "park switch" on the tranny. If this goes out, it will not allow the engine to rev over 3000 rpm making passing impossible. Cost $800 at a dealer to have fixed.

Posted on Feb 15, 2009

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