Thomas Neels

I have a2013 chevy tahoe transmission went out. I bought a used 6l80 transmission. Installed it. Only one problem. After I go say over 45 or so and then come to a complete stop for a second it feels like somone is rear ending me. Once I tried to go and the truck reved up then slammed into gear. I was wondering if this transmission needs to be flashed or relearning program hooked up to it. Please help i don't know where to go from here. This uses transmission is out of a2013 silverado