UPDATE:
I got the shifter (SLA) yesterday, I got it installed today. I still had no engine codes or anything so I cleared the one DTC in the TCM I had left since the last time I cleared the DTCs before installing the new shifter.
Now, with everything plugged in except the radio and window button connectors, the dash recognizes the car is in gear. As soon as I turn the key to on it says P and with my foot on the brake I can shift gears. HOWEVER... when I go to start the car it does NOT attempt to crank. The first time I turn it to start it doesnt attempt to start and then after that, it will not let me turn the key beyond on - to start again unless I remove the key and try again.
Just to confirm, starting attempts were made while the car was in Park, and my foot was indeed on the brake. I moved the wheel back and forth and the steering wheel wasnt locked, I can shift in and out of park and the dash recognizes the gear its in.

So...any ideas whats happening now? Thanks in advance!!