Transmission, automatic, 6 speed, HMD, 6L90

Years 2009, 2014–23 Models 5 Factory citations 11

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Also described as Transmission, 6 speed automatic, heavy-duty, electronically controlledTransmission, 6 speed automatic

Also documented for Cadillac Chevrolet

Documented applications

Savana — GMT610 (2003–2027)

2014–2018, 2022–2023 Factory-verified

printed only in the Upfitter lists shared with the Express

GM factory document — 2014 chevrolet gh van elec bbm si brief, p.7.
GM factory document — 2018 chevrolet 18 express savana bodybuilders sm 2017nov06, p.16.
GM factory document — 2022 chevrolet 22 express savana electrical body builder sm en us 2021oct12, p.13.
GM factory document — 2023 chevrolet 23 express savana body builder sm en us 2022sep13, p.14.

Sierra — GMT900 (2007–2013)

2009 Factory-verified

GM factory document — 2009 gmc sierra 2wd rpo code list, p.1.

Sierra HD — GMT900 (2007–2014)

2009, 2014 Factory-verified

the 2014 guides call it a heavy-duty 6 speed automatic with tow/haul mode; gasoline engines

GM factory document — 2009 gmc sierra 2wd rpo code list, p.1.
GM factory document — 2014 gmc sierra 2500hd fleet order guide wayback, p.4.
GM factory document — 2014 gmc sierra 3500hd fleet order guide wayback, p.4.

Sierra HD — K2XX (2015–2019)

2015, 2018–2019 Factory-verified

overdrive, tow/haul mode, cruise grade braking and powertrain grade braking; with the 6.0L V8 (L96 or LC8); 2015 marks: Sierra, SLE, SLT: S; 2018: GM's 2018 Sierra 2500HD order guide; 2019: GM's 2019 Sierra 3500HD order guide

GM factory document — 2015 gmc sierra 2500hd fleet order guide wayback, p.4.
GM factory document — 2018 gmc sierra 2500hd order guide copy gm authority, p.3.
GM factory document — 2019 gmc sierra 3500hd order guide copy gm authority, p.3.

Sierra HD — T1XX (2020–2027)

2020–2023 Single-source

with the 6.6L gasoline V8 (L8T); GM Authority 2020 to 2023 Sierra HD pages list MYD in the powertrain table

This page aggregates every documented appearance of MYD in the GMC reference. Confidence and citations are shown per application — the same code can be better documented in one year than another.