if all i did was hwy for a week straight over 30 miles a day type driving. id be in the mid 20's, and then it would stay up there for quite some time before the avg starts to tank on the dic when back to full time local crap.

reset your avg, then drive 30 mph and stop every 1/4 mile to 1/2 mile, idle for up to 5 minutes or longer ( some lights suck bad here) your avg will not be to high driving like that.