If Simul8 has become very slow at the end of a simulation run or while resetting the clock this is because Windows has placed a large percentage of the data about the simulation run on disk because it ran out of RAM.
Reduce the number of Simulation Objects that save results information. Typically
most simulations only need to collect results on 10% of their objects - Simul8
defaults to collecting results on all objects.
Reduce the length of the Results Collection Period. This is only possible if
your simulation is running from longer than is necessary for valid results to be
collected.
Increase the Results Synchronization Interval. The default time interval is 5
time units. If your Results Collection Period is long (100's of times
this) then you can probably increase this interval substantially and still
obtain accurate results. Find out more about this here.