transmission problem on 2000 GMC Yukon

I had a new transmission installed in my 2000 Yukon and it is having trouble still shifting into any gear but drive and reverse. Could this be a wiring problem? Or could it be something else?

Asked by for the 2000 GMC Yukon
It could be the TCM transmission control module or a sensor somewhere i would get the Transmission diagnose with a special scan tool to try to find the problem