Trans issue: 4L85e shift problem

[68GMCCustom]

Background:
I have a GM Performance Parts 4L85e behind an LY6 6.0L swap and using a B&M truck MegaShifter to shift it and maybe 1k miles on it. Both were brand new when installed. When I 1st installed the LY6 it was carb'd and ran a (built?) 200-4r. Well the 200-4r couldn't handle what the LY6 was putting out so I put in a 4L85e to replace a 200-4r (which the MegaShifter was bought for originally) and it shifted manually thru all gears just fine. Over time, I have lost the ability to pull it down manually to 1st...though while shifters in 3rd or Drive it will downshift to 1st just fine (from roll or stop) and 1-2 shift fine. But when I try to manually pull it down to 1st it stays in 2nd. I have adjusted the cable at the trans numerous times trying to fix it but nothing changes. With the cable set about as good as possible in Park and 1st... its slightly too long while in D (from 2nd to Reverse wont allow the pin to slide in and out, just P and 1) I tried again yesterday and didn't even get to test drive it. I setup my AeroForce gauge to display gear selected and from 2nd it wouldn't pull down into 1st now matter how I tried. Only difference since when it worked is about a thousand miles of use. One interesting side note and possible diagnostic lead...I sometimes feel like when in N and reving the motor that the truck is trying to move forward a little. Haven't verified this on flat pavement tho.

So my questions...
Theres no reason something in tuning would develop to keep the ECM/TCM from selecting 1st is there?
Or is it just my MegaShifter cable already needing replacement?
Could I somehow have damaged my brand new trans with the shifter adjustment being a bit off, without knowing it since all was fine to begin with?

Thanks for your thoughts!

If I put this in the wrong spot please move it Admins.

[72MARIO]

I don't have the how to answer for you to fix it.but it's in the tune preventing the down shift manually to first. The pcm will not allow you to drop to 1st untill a set speed. There is a you tube video on how to change the settings using hp tuners.

My stock 4l80 will up shift to 2nd in 1st gear above a certain speed and will not drop down to first untill somthing like 25 mph.

[72MARIO]

https://m.youtube.com/watch?feature=...&v=Erv5I29Ctrs

Here ya go

[68GMCCustom]

Thanks....but its not manually going into 1st even when sitting still...I guess I didn't make that clear. It will kick down to 1st when it should....this is a manual shift only issue.

[ls1nova71]

There's nothing in the ECM or TCM that's going to make it not manually go into first, it has to be a shifter issue. Sounds like the detents in the shifter dont match up with the detents in the transmission.

[68c10airstream]

I'm on board with ls1nova on this. Get someone to be in the cab and work it through the positions with the truck turned off and you watch from underneath. I believe you need to move either the pivot point on the steering column in/out or the same on the trans external arm. If the cable isn't moving far enough no matter where you put it, the column arm needs to be longer in length away from the column, or relocate the trans arm pivot point inward closer to the center. 6 of one, a half dozen of the other. Good luck.

[Hart_Rod]

Dumb question, but I'm going to ask. Are you getting any trouble codes?

[68GMCCustom]

I checked and there were some old lean fuel codes but I cleared and didn't some back.
I have a scan/gauge that shows me lots of things but set to the trans shows going into all other gears but not 1st. I'm thinking my cable stretched.