39 is Conventional non-Positraction Differential 3.55

My camper with the C6 has 3.54 and I always cruise at 60 and sounds like it's turning ~2500RPM witch I find it's the sweet spot for my application and I get around 11-12 mpg out of it on a nice road with mild wind.

Anything over 60 however, mpg decreases rather quickly.


If you pick-up is well tuned and you keep it around 60, OD with 3.55 you should see close to 20mpg!