Transmission slams into 1st SOLVED

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jared999

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Picked up a 2020 Tahoe PPV with around 98k miles.

From a stop, if I smoothly accelerate it shifts great into 1st, no problems. After I'm in first, I can punch it and all gears will shift normally.
If I do anything but that, it slams into first gear, then the rest of the gears will shift normally. The vehicle down shifts no problem.
I drained and filled the tranny, replaced the filter and installed a new bypass valve. Not because of the hard shift, but because I don't know the service history and because I wanted to install a new updated bypass valve for temperature reasons. The issue still occurs after the service.

Is this a computer issue, or an internal tranny issue, or something else? I've searched the forums and the Internet but it seems like the issues are 1st + reverse, 1st and 2nd, or downshifting, or the 8 speed and not the 6 none of which apply to me.

I did hook up my scanner but its not kicking any codes. Seems like the next step is taking it to an independent shop, the stealership or a tranny shop.

other info:
Engine idles evenly, but the gas pedal seems overly responsive to me. Perhaps that is just the type of vehicle (PPV) I'm driving. That or it's just very different than my 09 Tahoe as it feels this 2020 has a lot more punch.
No problem with reverse.
6 Speed tranny
 
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jared999

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In case it helps someone in the future:

The issue was a bad torque converter, covered under GMC warranty.

Had a new one installed and it shifts as expected. Throttle does not make the car jump like it used to, so that was definitely the torque converter too.
 
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NickTransmissions

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In case it helps someone in the future:

The issue was a bad torque converter, covered under GMC warranty.

Had a new one installed and it shifts as expected. Throttle does not make the car jump like it used to, so that was definitely the torque converter too.
Sounds like the stator (one-way clutch assembly) inside the converter was defective and slipping. Glad you were able to get it resolved under warranty.
 

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