2012 Yukon Denali 6.2L 6spd transmission hard shift from 1-2. Shakes truck

[testdepth]

This is the stock transmission and nothing has ever been towed with this vehicle. Less than 200000 miles on it and never been off road as its a kid hauling grocery getter. Recently while on a trip to North GA I noticed while taking off from a dead stop the car shifted hard from 1st to second. Hard enough so my wife asks "what the hell was that?". It shuttered the truck and was fine the rest of the day. It's intermittent but very noticeable when it happens. This only happens in 1 to 2 leaving from a dead stop at a light and not when slowing down to stop. Only on acceleration. I recently read the codes on this truck and found none for the transmission.

What can cause this?

 

[Joseph Garcia]

@NickTransmissions

 

[NickTransmissions]

This is the stock transmission and nothing has ever been towed with this vehicle. Less than 200000 miles on it and never been off road as its a kid hauling grocery getter. Recently while on a trip to North GA I noticed while taking off from a dead stop the car shifted hard from 1st to second. Hard enough so my wife asks "what the hell was that?". It shuttered the truck and was fine the rest of the day. It's intermittent but very noticeable when it happens. This only happens in 1 to 2 leaving from a dead stop at a light and not when slowing down to stop. Only on acceleration. I recently read the codes on this truck and found none for the transmission.

What can cause this?

Harsh 1-2 upshifts can be a few things:

1) Intermittent transmission fluid pressure (TFP) switch fault in either TFP 1 and/or TFP 5 - the pressure switches are located on your TEHCM and can be resistance-tested via a multimeter
2) Sticking/worn 2-6 clutch regulator and regulator gain valves in the upper valve body
3) Sticking/worn compensator feed regulator valve in the lower valve body
4) Worn/sticking main pressure regulator valve in the pump cover
5) Converter

1 through 3 can be tested/diagnosed by dropping the TEHCM/Valve Body assembly from the trans while it's still in the vehicle. 4 & 5 will required removal and partial disassembly so if the TEHCM and Valve body are evaluated and no faults identified, the transmission will have to come out and at that point, be overhauled.

Have you noticed anything else beyond the harsh 1-2 shift?

How many miles on the trans?

Visit my 6L80 Information thread for more information, including a quick tutorial on testing your TEHCM using a multi-meter. Ill be putting out diagnosis and trouble shooting videos showing that process and more within the next couple weeks.