Stored Procedure slow after weekend
Most likely activity on the server over the weekend has caused your data to be evicted from memory. This is just the way life is in a shared environment with limited resources. It would be good to understand what's happening over the weekend and how your usage affect other users of this service.

You could schedule a job for early on Monday, before anyone is in the office.  It would run your SPs with the various parameter values to warm up the bufferpool with the data you will be using.  This will evict whatever is in memory currently, slowing the process that is using it.