I don't think that's it. It could possibly be the modem. If they tell you your on 100 MBPS Service then that's what speedtest should be close to not at 29.
If your not getting the 100 MBPS then it's either the Modem malfunctioning or the ISP is throttling the Bandwidth. In Canada Throttling the Bandwidth is against the law. I don't know about whether it is in the USA or not.
I'll make a test page with 15 images on a page reduce the size of the resolution then have you try it and see if that makes a difference.