Long Lag On Some Sites

I'm having the same problem mentioned in this post where my speed tests seem fast but there is often a huge amount of lag when loading certain websites, particularly google but sometimes even on xfinity pages themselves (I see requests simply timeout).

I'm using my own modem and router and tests suggest it's not a problem with either the router config or the modem*.  Anyone else besides the original poster and the recent followup having similar issues? Solutions?

I figure it's either some kind of account setting, an attempt to introduce clever caching by xfinity that I've routed around (e.g. because I'm using google's DNS servers) or it's an issue with the way xfinity's network is configured in this area. On edit it occurs to me that it could be that xfinity is dropping packets in between my recently wired for xfinity apartment complex and the rest of their system.  Anyone else having this issue?  Solutions?

Even if you don't have a solution if you are experiencing a similar problem please reply with your general location ( I live in the city of Auburn Hills outside Detroit) since it might be an issue only affecting this region (e.g. poorly configured google co-location) and if we can narrow it down maybe we can get a network tech to take a look at it.

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*:  I'm using the same router config I had before switching to xfinity where this problem didn't occur (though frequent outages did) and it doesn't seem to happen when I use wireless data on my phone.  I've also ran both speedtests, pings and traceroutes that convince me that either the delay isn't between me and xfinity (small possibility it's an extreme heisenbug).