It's been awhile, but I've managed to do lots of testing, both on my main feed and through a VPN service I have.
I also noticed after watching carefully over the last 2+ weeks, that certain times of the day I get load of 'disconnects' and the like.
Final upshot is, Comcast appears to be 'mucking around' with Sling traffic, just like they do with Peer-to-Peer, jamming the bit traffic with all sorts of 'messages' to disconnect and mess with the bitstream. Once I put the Sling traffic on my VPN, it all 'magically' goes away, and things run straight and normal. The only problem is that I have a limited amount of VPN bandwidth (limited by my h/w router, not the service I subscribe to) and although about the maximum that I've ever seen Sling use the bits (around 5Mb/s+) is within the capability of my current h/w, a 'new' box to ramp up that VPN 'pipe' is another $400 or so, so I can't do my 'ordinary' stuff while doing any Slinging.
Hopefully will be moving in the next 6 months and get on another provider, with tons more bandwidth (actually 10x more and half the cost of Comcast) so I guess I'll have to continue with my current work-around until then.