2006 Yukon XL DENALI only getting 9mpg hwy.

What is your question?

We just bought a 2006 Yukon XL Denali and we are only getting 9 mpg HWY. What could be wrong? no lights are showing but there is a smell of burnt antifreeze in the car.

How long has your 2006 GMC Yukon XL 1500 had this problem?

We just bought it today but we also have a 2004 Yukon XL and it gets 20 mpg highway