Ls3/4l65e
 

Hello: I am new to ths forum and new to the LS swap.I purchased a GTO that came in pieces. It has Corvette LS3 engine and a 4L65E transmision and the harness thatis suppsed to operate te two is a Painless Performance haress. I got the drive train in and running but it shifts 1234 before the car gets to 10 MPH, and then it will not downshift untill the car comes to a complete stop. I have purchased HP Tuner license and software but I can not figure out what needs to be changed to make this work properly. As I said I am new at the LS swap stuff but I have chagned everthing I can find that relates to the transmsion and nothing fixes this problem. I am hoping someone will have had the same problem and fixed it that could tell me what to change in the ECM programming to get this thing to shift.