Need help re. Jeep catalytic converter...

-Do you recall ever experiencing spark knock(pinging)? If, for what ever reason, the computer has pulled out timing,and hasnt put it back yet, that would definitely negatively affect fuel mileage.
-So will a too-cool coolant operating temperature, ie, a failed t-stat.Or a slow MAP sensor.
-Or short trips, or soft tires,bad alignment,extra weight,elevated ride height,driving style, driving below TC lock-up rpm,dragging brake calipers, extended idle times.....