Tune or gear swap.

[07Burb]

Tune

 

[ccapehartusarmyINF.(ret)]

you dont need a tune the only time yer speedo would be affected is if you put on tires with a larger overall diameter then your factory tires
a 3.73 was available on a 97 yukon 2dr diesel model the gas models came with a 3.08 or a 3.42

 

[metaljunkie]

Has anyone here switched from 3.42 to 3.73? If so how much of difference did it make?