drivetrain and rear end modifications for a 9" lift

I have an 06 LT2 ext cab z71. I plan on lifting the suspension 6" and the body 3" in a couple weeks. I may throw 35 or 36" tires and 19-20" wheels. My question is what should i do with my drivetrain and rear end? My truck will strictly be a show truck with very minimum dirt time. I have heard i need to get a custom drivetrain and a better rear end (i think its a 3.42 whatever stock is). Is this true?