[cdnus]

Where is your msd box mounted?
Does the shutdown occur at speed or when you are in traffic or driving very slow?
Is this happening when the ambient temperature is high, if so have you tried driving in cooler temps, eg. Cool evening temps.
If your box is mounted where it will get too warm it will send erratic tach signals and could cause temporary shut down.
A quick test is when it shuts down quickly and carefully put your hand on the box, if it is too hot to keep your hand on it, it is probably the cause of the shutdown.
I chased this gremlin for a year and eventually solved it by relocating the box.
Hope this helps
Craig