Raymond Andong

i have a 2017 Sierra1500, 5.3L crew cab, Vibrates at 85, down shift clunk and on take off, Dealer says there"s nothing wrong, 71,000 miles on it and Transmission goes completely out while I'm on freeway! After a fight they put a new trans in, i had it back for less then 2 months, not even long enough to get oil changed and having the same issues. They wont even check driveshaft after my probably 5 th request, i really like thes trucks but i got the Lemon, totally baffled...