Rusty,
Do you have another motor or speedo to swap out? If you can swap one or the other, you may be able to ascertain which of the pieces is giving you issues. Also, when the truck shuts down have you paid attention to which of the LED's are on or flashing?
Here are links to the track guides which may help you diagnose your issue:
Newer Activ8 with SuperTuner software:
http://teamnovak.com/file_download/1...TrackGuide.pdf
Older Activ8 without SuperTuner:
http://teamnovak.com/file_download/1...rack_Guide.pdf
If you cannot determine the issue that way, give the folks up at Novak a call or email...
Wilde