In 2005 we had a 3/4 ton avalanche 4X4 with then 8.1L and might still have it today but wife & I wanted a 5th wheel. Traded for a 3500HD dually with the Duramax 6.6. Saved on the MPG but that gets offset some % with the gasoline verses diesel prices.

 

re read this thread and realized I didnt put ny rear in #s in. m running 4:10 i the rear... This thread is timely.... I did another 1K mile round trip road trip, unloaded. drove 452 highway miles on one tank used 34.5 gallons and averaged 13 mpg.I still love this truck. Just at 100K in miles.

 

FWIW
I tow a travel trailer that is about 9K I gert about 8.6 mpg when loaded in the mtns

 

I realize this is an old thread but I'd thought I'd chime in. Our 2005, K2500, 8.1L gets 13 mpg on the highway if you travel 65 mph. Lower mph -> slightly higher mpg.


When we tow our Airstream travel trailer the mpg is closer to 9. Drops a little in the mountains, gets a little better on flat land.


4.10 rear end, automatic transmission.


on edit... our similarly equipped 1996, C2500, 7.4L, 4.10 rear end gets very similar mpg