Car shakes at 50 mph after replacing transfer case

What is your question?

My Mariner hybrid has started shaking at 50 mph and faster after we replaced the transfer case. It did not shake while driving before the repair, only made the clanking noise from the ruined t case. I have already checked to diagnose the shaking where the driveshaft goes into case and where the driveshaft goes into rear end, and the center driveshaft bearing that I also replaced and the bolts that go into transfer case and was able to tighten them quite a bit. After all that the car is still doing the shaking at higher speed. Is there Anything else it could be?

What makes this problem better or worse?

Only happens at or about 50-55 mph and stops if slow down

How long has your 2006 Mercury Mariner had this problem?

About a week