I bought this car with a disconnected elec connection on the trans it drives but it appears to be in top gear.

I didnt notice the connection was disconnected, The car drives good with a smooth idle.
The car goes forward and reverse with the plug undone.
when I plug in the "D" shaped plug in to the trans I get no forward movement, But reverse works normal. The check eng light is on and codes read shift solenoid 1 2 and 3 also torque converter clutch The trans fluid is not burned but, it didnt look new either.
Can the problem be the 3 shift solenoids?
and if so whats the chances all 3 went bad at the same time?
I checked the connection and found groung and power at the connection in multiple pins.
Thank You for your help.