OK,
By disconnection the harness you bypassed the electronic shift solenoids so the PCM can not shift the transmission. You are basically in limp home mode (by default 3rd gear). The real problem is you also discoâ??d your line pressure regulator. Without the regulator you are subjecting you trannyâ??s hydraulic system to extreme pressures that will cause it to fail for sure!
You can not trouble shoot an electronic controlled automatic by the seat of your pants. You need to run a full power train diag and hydraulic system pressure checks before you do anything else. This requires test equipment and technical knowledge of the ATX and PCM.
If you really want to try to shot gun it, replace the range sensor. Based on your descriptions it is the most likely component, the easiest to change and the least expensive. You do not want to try and change the solenoids with out a manual and some good tools.
jeff