Speedtests totally erratic - yes no ping or download or upload - timeouts

[glnzglnz]

The last week, speedtest.net from my PC has been totally erratic.  Some tests to local servers are right on target, with low pings and down and uploads per my expectations.  Other tests time out on ping or suddenly have much longer pings to the same servers.  Some down and uploads are OK and others time out.  All over the map.

In addition, my wife's MacBook Pro - on her Mail app - keeps showing error messages on all her email accounts simultaneously.  She has to Quit and restart Mail - and then it happens again after a while.

Never seen any of this before, after years with Verizon DSL.

I'm on Verizon Home DSL in NYC rated for 7Mbps down and 750kbps us.  I'm on Fastpath with Verizon.  My PC is Win XP Pro SP3 (32-bit).  My modem router is an Actiontec GT784WNV.  My PC is wired into the Actiontec, and my wife's MacBook Pro and iDevices are WiFi into the Actiontec.

I have run numerous anti-virus, anti-rootkit and anti-other-malware scans, with Avast (including a boottime scan), MalwareBytes, TDSS killer, Windows Malicious Software Removal Tool, etc.  I have run sfc twice - scannow and scanonce.  I also have SpywareBlaster and Spybot S&D.

My browser is Firefox latest with NoScript, Better Privacy, Disconnect, AdBlock Plus and tight control on cookies.

I have done ipconfig /flushdns numerous times.  Have rebooted the modem-router numerous times.

So, what is it?  What is causing these issues?

Thanks.