97 Ultra 680 Questions

Help,...I've got a 97Ultra 680 SP with single pipe,.....it has many miles on it, seems to run well when it's cold -20c , but a dog when she warms up to 0c. Had it out today when it was warm, lucky to get 90mph out of her on hard pan, I remember 100+ last year........ today it was turning 8000rpm...only 85 to 90mph...........by the way getting 7 miles per gallon. What's up Belt? Jetting? what kind of performance should I be getting? Horsepower ? Speed? Mileage? Your input greatly appreciated.
Thanks,
Darrell