Look into changing gears closely before having the work done.
Tired having a the gears changed on a 2013 Tahoe from 3:08 to 3:42 gears. The shop tried seven times with six different sets of gears and could never get it to work right.
The new gears would make a high pitch noise. I called GM and they stated that everything is tied into the computer and the computer would have to be changed out also.
I was lucky because the shop refunded all of the money paid and put the Tahoe back to stock which ran great after putting the 3:08 back in the Tahoe.