2010 Sierra

[GMC or nothing]

Do you think my GMC 1500 has the Allison trans? It has a 5.3 with the tow package and manual mode. When I shift to tow mode it REALLY makes a differance in the gearing and slows down if I have a load so I don't need the brakes as much on a hill.

 

[Molson02536]

Do you think my GMC 1500 has the Allison trans? It has a 5.3 with the tow package and manual mode. When I shift to tow mode it REALLY makes a differance in the gearing and slows down if I have a load so I don't need the brakes as much on a hill.

Nope you have 4L60E transmission in your Sierra, you can check with that in your PRO code sticker in your glove box. The code will be M30 on the sticker.

The Tow mode just drops the voltage down to your EPC valve to raise the transmission line pressure up. The rise of the transmission line pressure gives the servo's more pressure to apply to the clutch packs.