Dan,
Actually, GPS time is currently 13 seconds ahead of UTC. This time offset only changes when UTC id adjusted with a leap second, as it last was on 31 December, 1998. UTC is always within one second of GMT. That is not to say that the time displayed on your GPS receiver is 13 seconds ahead of UTC. Most, it not all, current GPS receivers will correct to and display UTC. The GPS to UTC correction is included in all the other orbit and time information in the GPS broadcast message, so your receiver "knows" how much to correct.