4L80e 6.0 E38 and T42 TCM shifts 1-2, 2-3 and stays in 3rd

[HiTash]

Hi

I have an interesting one here,

Impala with 6.0lt and 4L80e conversion done here in Australia, Car came to me with the 4L80e in it but TCM and harness was 4L65. (It was simply stuck in 3rd gear)
I've changed the TCM and harness to suit (File attached) I've also changed the internal harness mainly because of and oil leak at the main connector. I also tested the TFP switch while the pan was off.
Now I can command any gear and TCC thru scanner up and down gears but when driven it shifts 1-2 and then 2-3 OK and at approx the right speeds but then it stays stuck in 3rd and will only change if I force it with scanner.
I'm not an expert on transmission stuff but definately not a noob either.

I need some help or pointers to see what im missing. I really want this car out of my shed.

Regards Ash
Wiring + Tuning Solutions

[Lakegoat]

Was the 4L60 transmission plug used on the 4L80 when you got it?
Did you use a conversion plug between the 4L60 plug and the trans when you started changing things? If so, the previous owner probably swapped the wires around in the 4L60 plug to run the 4L80 and used the gen 3, 4L80 wiring pattern instead of the gen 4 pattern. Now the conversion plug is plugged into the wrong pin pattern. You also need the ISS plug---do you have that, some 4L60's did not have an external one. It's disabled in the tune. It's not the trans since you can shift it with the scanner.