4l80e trans t case ???/issues

[BigFrank]

 have a 4wd suburban   if ya take of at a reasonable rate  and right around 50 + mph  gets a bad vibration  like yer running down the rumble strip  trans goes into  od and goes away but  any slower than 60 mph it wants too make a bad vibration  i f i take off in D  and then shift too od it does it bad        abud of mine  told me theres a keeper snap ring that  will come off in the t case and  cause similar  vibrations