Slow browsing to one specific folder over VPN connection

I have a remote office that is connected to the main office via a hardware VPN. Both offices have Sonicwall devices and the VPN tunnel is between these two devices. Connection speed is alright access the exchange server with outlook, using the printaudit software, timesheet software and folder browsing .... except one. There is one folder on one of our NAS servers that contains a large amount of project folders. Everyone has the drive mapping of P: pointed at the folder right above the folder with trouble. They can access the P: drive but when they try to go to the projects folder, it hangs. Maybe 10 minutes later, it will come up. (this is in explorer) The problem folder contains 245 subfolders with a very large amount of subfolders under those. Now the tricky part, if you happen to know the UNC path of one of the subfolders, you can go to Start > Run and type it in and it will come up rather quickly. If you go into the command prompt, you can browse through the P: drive and do a dir of the problem folder with no problems.

Things I have attempted:
1. I made the pc at the remote location a master browser by editing the registry.
2. I checked all DNS and WINS settings even though it is only one folder with trouble.
3. I have knocked down the encryption settings on the VPN tunnel to reduce the overhead on the tunnel.

Specifics about the setup:
- The pc is windows xp sp2 with all of the updates except IE7.
- The server is Server 2003 with all the service packs but may be alittle behind on updates.
- The main office has a full T1
- The remote office has a 3M cable connection.

Any ideas would be greatly appreciated.