The STT doesn't have an internal guider does it? Only the Remote Guide Head?
The RGH should be able to trigger the shutter with each exposure regardless of what the main shutter is doing. I'm somewhat certain that is how my STL works with the RGH but to be completely honest it's been about 4 years since I used the RGH with my STL.
A while back SBIG changed their meaning of "Internal" and "External" guiders. It could be that we think the RGH for the STT is an external guider? In SGP do you select "External" or "Internal" for the guider settings in the SBIG settings?
Thanks,
Jared