The GTech finishing speed, and a track trap speed are two different things. At a track, you pass by two markers (spced apart obviouslly) at the end of the track, and based on the time taken to cover this distance, your trap speed is calculated. So at the track, it is not the speed you're finishing the 1/4 mile with, but rather an average of the last X ft. (I forgot the exact distance).. The Gtech, calculates your speed once at the end of the run, so it will obviouslly be a tad higher..
gee I hope that made at least a little sense