A little more info could help:
do you have a server? if so, what is its operating system?
how did you set up the VPN? are you using 3rd party software?
what types of hardware firewalls are in place?
I suspect the issue has nothing to do w/ AC, nor w/ your T1 connection speed. These types of issues are usually networking issues, and the most complete information you could give us would help. Perhaps a diagram of your network....
i.e. internet-->firewall-->server-->clients (main office)
^
|
VPN
^
|
firewall-->network switch-->clients (offsite)
What does your system look like?
