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Stack Shifting: 4l60e

Blazerblitz

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Blazerblitz Enthusiast

Blazerblitz

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Posted

Long story short,

I probably have a bad TCM or screwed up wire harness that's causing my transmission to stack shift (shift from 1st to 4th very quickly and not kick down when you take your foot off the gas).

I payed a guy to do some special testing for me, and he's baffled. He logged into the computer, verified the stack shifting, and then when he logged off, it started shifting normally.
Next, he shut the truck off, let it sit for a spell, and started the whole process over again. It was stack shifting again - right away - while logged in, and then after logging out, it worked normally until the truck was shut off again.

He contacted HP Tuners and asked them what this could be and they were not really sure, so between them and his professional experience, they think it's the harness or TCM. Any other ideas?

The only thing I did to the 4l60e that isn't stock is I replaced the stock servo with a Corvette servo. I kept the stock pin, though. Nobody says that this would cause the stack shifting or make the weird tuning issue of canceling out the stack shifting occur.

This is driving me nuts!

  • 8 months later...

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