The original (Free) GPSAR v3.3 does not read the newer .sbp and .sbn file formats from the GT-31. To use it you will have to convert your files to .gpx and may lose some data accuracy.
GPSAR-Pro is adapted for the new (more compact and contain more accurate data) file formats.
RealSpeed and GPS-Results and GPSAR-Pro are the preferred software packages for use with the GT-11 and GT-31 and for GPS-Speedsurfing.
The older I get, the better I was.