95 Jimmy

I have a 95 GMC Jimmy, it is an automatic, 4x4. Recently it would start, but not move when in drive. Learned that there was water in transmission fluid. It was partially flushed and now needs to go through the machine for complete flush. Tech said transmission was not ruined. this just happened and taking it for flush this week. However, today it starts, then shakes and dies. What is the problem? Please help.
thanks Kelli