If speedo- and odometer-readings don't match up than your speedogauge is off/failing.
On long trips I always recalculate the actual miles travelled by plotting the entire route in Google Maps.
Lean out the primaries for better AFRs.
Your dynorun was mostlikely made with an open hood.
Any chance the airflow into the engine gets smothered by a clogged airfilter or hoodclearance?
