Latitude 6320 - Wifi Slowdown in computer

I have been frustrated with a WIFI slowdown on the 6320.   Example: Today my download speed went down to 5MB using Speedtest OOKLA.  I rebooted computer and speed went up to 60MB.  Later same thing happened, I rebooted and speed went up to 80MB.  Upload speeds seem remain good somewhere between 5 and 8MB.  This has been going on for several weeks.  I thought problem was WIFI network but could not diagnose any problem and other computers seem to operated normally.   So just yesterday I discovered that a complete restart will restore speed to a comfortable normal.  It is peculiar that download speed suffers so much, while upload speeds are not so affected. 

Other than buying a newer computer what can I do.  I would like to diagnose problem.  Can't see anything abnormal running in task manager.  Don't other tools to use to find out what is grabbing my Wifi.