Our 2016 GC Summit EcoDiesel (purchased 10/2016) completed a 5,227 mile summer trip throughout the west and northwest. The GC performed flawlessly averaging 31.3 MGP overall. Travel was city, highway, mountain (much of which was above 7K feet) in heavy traffic and included 80 MPH speed limits. The GC Summit began the the adventure with approximately 10K miles. The Summit performed best at speeds of 74-77 MPH.