The 6.0 gas engine in the GM TwoMode Hybrids are rated at 332 hp plus they have a 65hp electric motor inside the Allison 2ML70 transmission. They are definitely not race cars but there is some fairly impressive power there for a "Hybrid" (This Boat will scoot when you get on the go pedal)
If I was not running a lift / oversize wheels and Nitto Grapplers and I was not such an aggressive driver I am sure that my mileage average would be better than the 18.2 MPG over the last approx 5k that the DIC shows. Once the war with Iran gets going and gas prices shoot through the roof we may all be wishing for a weak kneed little Prius (penalty box) to drive LOL
27mpg on the highway yesterday

just use 91/93 octane the vehicle responds better with it...
the Engine timing will advance to about 40-42° degrees in v8 mode
and upto 20° in AFM mode (87 octane retards the timing so AFM is not seen very much or may cause a malfunction of AFM or AFM loop of death in which the vlom solenoids rapid fire tell the afm blows it self apart "catastrophic failure fashion" i.e no compression & oil consumption/oil hydro-lock )..
this mostly applies to the VVT enabled GMT900s such as the hybrid and yukons..
that is driving crappy like other drivers
with peak speeds of upto 90MPH (speeding up on the down hill to get up the next hill) this saves a ton of fuel.
I tried pretty hard with 87octane 18.5MPG(city and highway) is pretty much the max you can get with that. .87octane at 27 miles would cost $5.20 a gallon
i rather spend 3.859 now and save $1.34 a gallon later
averaged 0.144¢/ miles @ $3.859 a gallon i think with a few Aero mods i could get to to about 32-35mpg on the highway No penalty box required.. that is 2000 accord or Camry class MPG
I noticed the light weight hood trying to lift up (or flap around in the wind) so that might be a good spot to deal with an Aero seal(weather stripping). possible adjustment of the leveler as well under body could use some work as well..
honestly there is plenty of room for improvement...