Need help with T1 connectivity problem

Here’s the situation:
New 1.5 T-1 installed last week. When I make an http request of my website or shopping cart back office function I’m getting on average a 8-15 second response delay. Any other url address is not an issue (excellent response times) and the problem only happens from the office computer network. No problems when accessing same website from other locations.

Traceroute shows some packet loss. The host server is firewalled but port 80 request is usually 8-15 seconds long. My hosting company is at a loss to explain it or solve it. T1 provider doesn’t show any problems. Any suggestions on possible solutions? Thanks.