Open loop idle in gear only

Trans am ls and 4l80 segment swap from a 1999 Silverado. Wierd problem that I'm hoping has a simple solution. Problem is when you put the car in gear it triggers openloop "OL-Accel/Decel". Put it in neutral and instant closed loop. Also if you give it some throttle while in gear you get closed loop. It appears only to be while you in gear and foot off the throttle that it will trigger an open loop idle. Moved pe stuff around and its still happening so help me brainstorm on what could be the culprit. No bad ideas here cause Im about out. Thank you.

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The vehicle platform type says GMT800, I don't even know what that is, lol, but it isn't an Fbody?

GMT-800 is 99-07 Silverado/Sierra/tahoe/surburban/yukons.
GMT-900 is 07-13 Silverado/Sierra etc etc.

Anyone ever seen anything like this?

No but surely it is something to do with the gear "selection" (drive/neutral, and maybe more) which is detected in an auto, presumably it's different between the vehicle/gearbox types and now detects the state wrongly?

good suggestion. It is a swap from a 4l60 to a 4l80 so could guess that the harness is wrong. Ill have him look it over. I was thinking maybe it was load related maybe?

I know this thread is 5yrs old - was there ever a solution found for this? I have one doing exactly this same thing......

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I know this thread is 5yrs old - was there ever a solution found for this? I have one doing exactly this same thing......

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I fixed it....

and the fix for the next guy that searches this problem is.......??????????

What did you find wrong?

Im having the exact same problem.