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Old 08-21-2020, 02:28 PM   #1
1976gmc20
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Question AT computer glitch?

We took the pickup to town today for some groceries and the lumber for the bed in the topper. It seemed to be shifting rough and late, and running too high RPM on the highway.

I checked the fluid in town and it was fine. Coming home it did just fine, running about 2100 at 70.

6.0 / 6sp. Is this weird or what ?????
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Old 08-22-2020, 07:56 AM   #2
Palf70Step
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Re: AT computer glitch?

No clue, but wonder if any codes got stored that could lead you to an idea.
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Old 08-22-2020, 10:59 AM   #3
1976gmc20
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Re: AT computer glitch?

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Originally Posted by Palf70Step View Post
No clue, but wonder if any codes got stored that could lead you to an idea.
No warning light on; I just have one of those cheap O'Reilly code readers.


Edit: I'm thinking that if this happens again, that I should just pull over and shut off the engine, and then restart and see if that "re-boots" the TCU so it works right.

The fluid was supposed to be fresh from the dealer, BTW.
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Last edited by 1976gmc20; 08-22-2020 at 11:06 AM.
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Old 08-23-2020, 01:13 PM   #4
yuccales
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Re: AT computer glitch?

Could "tow/haul" mode be on, but light off?
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Old 08-23-2020, 10:00 PM   #5
1976gmc20
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Re: AT computer glitch?

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Originally Posted by yuccales View Post
Could "tow/haul" mode be on, but light off?
I don't think so but I haven't even tried to use that even when we brought a u-haul trailer back from CO. I forgot all about that and it didn't seem to mind.

Even in tow/haul mode it should still go into OD, right? Was running almost 3K at 70 mph going to town.

I should try it out and see if the light works and what if any difference it makes.
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Old 08-23-2020, 10:52 PM   #6
yuccales
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Re: AT computer glitch?

Quote:
Originally Posted by 1976gmc20 View Post
I don't think so but I haven't even tried to use that even when we brought a u-haul trailer back from CO. I forgot all about that and it didn't seem to mind.

Even in tow/haul mode it should still go into OD, right? Was running almost 3K at 70 mph going to town.

I should try it out and see if the light works and what if any difference it makes.
I'm just throwing ideas out there, but your rpm's seem a bit high. Hope you get it worked out.
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Old 08-24-2020, 11:08 AM   #7
1976gmc20
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Re: AT computer glitch?

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Originally Posted by yuccales View Post
I'm just throwing ideas out there, but your rpm's seem a bit high. Hope you get it worked out.
More than a bit high. Normal is about 2100 at 70 mph, which is what it was coming back from town. This is an HD with 4.10 axles.

I thought the transmission was just cold, but it's ten miles just to get to the highway. Should be fairly well warmed up by then. Unless there's some sort of sticky solenoid, I feel like it's in the computer.

I prefer stick shift but I have to say that this six speed a/t works really nice. It doesn't "hunt" gears going up hills and it will actually shift itself down and hold you back when you let off the gas going downhill.
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