Can someone please explain this to me?

I left Charleston WV for Wilmington NC a couple of weekends ago. When I got to Raleigh my trip computer said 20.0 mpg. By the time I got to Wilmington it was down around 17.something. Charleston to Raleigh is not at all level. Raleigh to Wilmington is prety darn flat.

Comming back, about the same thing happened. When I started getting into the mountains the mileage began to climb. I was around 17 even at Raleigh again but by the time I got home my overall trip was 18.7 mpg.

I really can't say my speed varied that much either since it was all interstate. I have a 2005 ECSB, L33 5.3L, 4.10 gear, & factory tires.

Could the computer be programmed for better efficiency at higher elevations?

 

After several trips from red river NM. I noticed my mpg was always better comming back. I figured it was because I was going down hill. I asked a Instructor at the Gm training center about it and he said [ the computer reads baro at start up and it will run at high altitude settings untill the next restart] It makes sense but he may have been full of