Differential Unit problems of the 2006 Lexus RX330

Transmission has a hard time selecting a gear between 2nd and 3rd. It starts to go into 3rd gear then jumps out for a second and then slams back into 3rd. Usually when lightly accelerating. Very noticeable. I have taken it into the dealer 4 times and was told I may just need a new transmission!! it only has 108,000 miles on it. I have never heard of this problem with a Lexus! that and the rear differential was diagnosed as bad as well! it's like the entire drive train is garbage!! very very disappointed with Lexus and I hope they will make this right with me. I don't want to be on a trip with my family and it break down on us when I payed for reliability.