Users experiecing disconnects accessing a hosted RDP application - need help troubleshooting the disconnects

I have been trying to troubleshoot RDP disconnects for users that are accessing a Hosted Insurance application.  

The network details:
Server 2008R2 domain controller
Comcast 100/20 Internet Speed (static ip)
Dell PowerConnect 48Port switch
Sonicwall TZ210 - connected site-to-site with a Satellite office (no issues with VPN)
Windows 7 workstations.

There were no issues with this until recently.  Not sure if it's a hardware issue or something else.

Here is where I am with this issue:
*Client upgraded bandwidth from 50/10 to 100/20 to try and resolve the issue thinking it was bandwidth - no change
*I have replaced the network cables from the Server to the Dell "unmanaged" Switch - no change
*I have replaced the WAN cable from the Sonicwall to the Comcast Gateway - no change
*I have replaced the LAN cable from the Sonicwall to the Dell Switch - no change
*I pulled the Sonicwall offline and threw up a Linksys Router for a few hours to see if the Sonicwall was the problem - no change

The disconnects are intermittent and seem to only affect the users of the installed RDP application.  The disconnects are not regular and happen at different times for users.  Most RDP connections reconnect after the disconnection however some users are also seeing a failure with a protocol error that closes out the RDP connection completely which requires the user to run the Terminal Services Shortcut again to relaunch the application.  Network activity seems to be good - other users (ones not using this application) can print, access files, access the Internet, etc. without issue.

I'm not sure what is happening and need some help at this point to figure this out.  

The Vendor has done ping tests through an affected workstation to the hosted application and was not seeing anything returning from Pingplotter.  I don't really know Pingplotter and since it was going through the Sonicwall with ICMP off I'm assuming that was why.  The Vendor thought it was the Sonicwall.  I disproved that when I put the Linksys router in place and users still experienced the disconnects.

Working with Comcast we plugged a laptop into the Comcast Gateway directly and ran pingplotter and Comcast reviewed the results and said things were good through their connection.  Comcast replaced their gateway at the beginning of this issue and don't believe there is any issue with their equipment.

I haven't replaced the Dell switch, made any changes at the workstations or made any changes with the Server2008R2 NIC card - it could be one of these at issue however I'm trying to work my way through this issue as methodically as possible - "one change at a time".

I am running Wireshark on one of the workstations now and am asking the user to tell me when she is getting disconnected so I can try and review the Wireshark results to see if I can gain any info at the time of disconnect - however I'm a Wireshark noob and don't really know what I'm looking at.

I'm stumped at where to go next with this intermittent RDP disconnect issue and need some help from the Experts Exchange community.  The client site is about an hour and a half away so I have limited access to the hardware for testing yet will do whatever I can to get this solved.  It's an annoyance for the users at this point and not a three-alarm fire however they are getting frustrated.

Any feedback and/or guidance would be appreciated!

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CTCSupportAuthor Commented:
I was able to solve this issue by replacing the Comcast WIfi enabled gateway (Cisco model) with an Arris Surfboard 6183.  Crappy Comcast Cisco gateway was causing the issues.  This took several months to figure out and I hope that this answer helps someone else down the road.  Very frustrating!

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