At that mileage and age, both chains should have been changed (recommended at 100,000 miles or 10 yrs which ever is sooner) so it would be prudent to do so asap if not done already.
The YH engines are more sensitive to stretched chains which can cause timing issues, as they have a cam timing sensor on the exhaust camshaft sprocket. This is likely to be the cause of poor mpg and sluggish acceleration.
🙂
Edit: This has been mentioned on one of your previous posts 'Sick Signum'.