184145 osCommerce Site analysis neede

For the past couple days (and on and off over the past year) customers have complained about our website loading verly slowly. We are pretty picture intense and have tried to keep file size small but we need detials high. Also, I've spoken with our vps people who say to upgrade to their next highest plan (which we did) but still our site seems slow. I need someone to take a look around and see what's really causing the problem with our site and our vps space. We have 4 different .com in a vps site that should easily handle the traffic. something is amiss and I need help figuring it out. osCommerce is crucial to our business, however, so I need someone famailiar with it so that any changes won't affect the oscommerce or that oscommerce can be immediately adjusted. We too have noticed a huge slow down in just the past few days. My vps people have done something on their end but it's not any better from our point of view.