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Manual Shifting a Automatic Problem?

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So I’ve searched all over and can’t seem to get a straight answer to what I’m experiencing. So  I have a Black Bear Tuned 03 GMC Sierra 1500HD with the 4L80E 4 Speed Automatic transmission with the ability to Manually shift 1-2-3.


My understanding is that when I Manually shift it down into 1st gear it’s suppose to lock it into 1st gear so it revs up way higher and engine brakes to slow down but does not shift until I manually shift up to 2 or 3 or put it back in Drive. Well when I lock it into 1st gear, the revs are much higher but it still automatically shifts to 2nd gear once I get close to 25-30mph even though I have 1st gear selected.
Is Manual shift lock not working for me?

Has anyone else experienced this? 
I just don’t get the point of manual shifting if it’s still gonna shift up automatically anyway 🤷‍♂️

Thanks for any input!


Edited by Monztruz
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The auto upshift to 2nd is just how they work. They weren't designed thinking that someone wanted to max out the speed in 1st.


It's possible that if you changed the settings to work on RPM only and raised the speed up higher in the calibration that is would hold the gear but then that might create another problem when you put it back in drive. It may tag the rev limiter and not shift correctly because now it can't reach that speed in 1st.


Likely you'd need to switch to a fully manual valve body and ditch the electronics if you want it to never shift.

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There are a FEW "Black bear" tunes. They are VERY NON descriptive on what they are, and do.

 I will guess they only adjusted the trans shift points. Then messed with engine timing, mixture etc.

 NO tune will disable the 1-2 rpm up shift. Even a Brand new GMC Denali will NOT downshift to 1st

when the cruise is on going down hill. ( decent control) .

 I am betting youll be doing a trans rebuild if you start to manually shift it if its got over 150K on it.

 Your 4 crew cab is Not a light truck.

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