Good luck. Not letting go of mine. I just put quartz-halogen headlights in it.
If it were the 1950s you could just take your cam to a cam regrinding shop and have it reground. Not sure about today.
Would you get ROI on a transmission swap? My XFi is only good for an indicated 65 or so. Compare the final drive ratios. Taller tires?
Something you might fabricate is the Eco light that comes on to prompt you to short shift through the gears. Or use a tach. The light is useful as a rough speedometer in the intermediate gears.