Shift pattern 6l80e 6l90e prnd321 prnd6d4d2d1

I'm trying to get a 6 speed auto to work in a Colorado canyon gen 1. With 58x gen iv motor.

Stock I believe is Prndm 21 which is actually prnd6 d2 d1
I only get the display to read prnd3 1 or prnd 21 on the Colorado dash.

I've fixed this in raw bin file code. To read prnd321, at cost though.. now the trans apears to see a different internal pattern?

Anyway my question is I'm a truck factory application will a 6spd auto hold 1st, or 2nd? If selected?

Anyone else play with 6spds with a 4spd dash? Whats the factory shift pattern on a vette? Prnds 21??