VPN Traffic works fine but regular Internet service is intermittent

Hi,

Using a cisco 1720 with one 10/100 and one 10bt WIC card, connecting to Alltel DSL with static IP address.  For some reason they provided two addresses in a /30 configuration.  At first I thought one was the GW and the other should be my router however, they apparently provide two usable address at this time in this area.  I confirmed this with Alltel tech support.  Anyway, using image c1700-k9o3sy7-mz.123-2.T.bin.  We have a VPN configured back to the main office that works just fine (20 other sites connect using essentially the same router config, some variation in connection types.) but these most recent connections both have problems connecting to the Internet, some web sites timeout, some come up just fine, usually the Internet access fails after a period of time, yet the VPN continues to function. (very strange behavior)   I suspect the image however this same image and nearly the same config works just fine with a cable modem.  The Alltel DSL requires authentication so a d1 interface is configured on the routers.  I have replaced the router with an identical one and had the same issue.  I am running out of things to replace or change out.  Has anyone seen this behavior before.  Any advice would be greatly appreciated.

Thanks,

bk