If you didn't correct the speedo then your actual miles traveled is greater than indicated by the odometer. This will throw both hand calculations and tthe DIC off toward the low side. Additionally, you could now be looking at winter blended fuel.
If you really got 23 at 70-75mph I'm envious. the best I've been able to manage is 22 at 65 mph. Is yours 2WD?
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510