vibration in rear end

I have a2013 chevy tahoe that I just installed a used transmission. I also had it programed since it was not shifting correctly. However there is still now a vibration that was not they’re before the transmission went out. I also changed the rear ujoint thinking that could have been the problem However it’s still there. I cannot figure out what is causing it. It only happens between 50 and 55mph. It may do it sometime while accelerating but it might just be me. any suggestions. Thanks

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