My 09 seems to switch constantly at 60mph-75 mph between V4 and V8 modes. Autostop and everything else seems great, but highway mileage is right around 20 on interstate, 20-21 mixed driving. I test drove an 11 hybrid Denali with no aero treatment, 22" wheels, steel hood, etc and it did better on the highway and seemed to stay in V4 a great bit more. I know the 11 was rated at 23 instead of 20 like the 09, and since there does not seem to be hardware changes I figure it is in tuning. Anyone try to update to later model tuning t improve mileage or function?

 

You can't update and that's a shame. Short answer, regulations.


The newer models have some slightly different hardware but yes it is mostly "tuning". They got better as they went.

The fact that you can get V-4 at 75 mph with a 3 Ton SUV is still way cool eh?

See if any non-hybrids will do that.