cycling problem

Trane tam7aoc48h41sba avg ext. temp 0 > -5 centigrate, temp setting 68 deg farhenit on programable trane thermostat, unit starts up and runs for approx 25 minutes, reaches room set temp and remains running while showing it has reached temp for awhile. shuts down for approx. 5> 6 minutes. so run time approx. 25 min. down time 5 minutes run time . seems to be to much run time, house is new , good insulation and no drafts, any suggestions