Wierd troubleshooting challenge: Constant buffering on playback, but live is fine...which solution to try first?

UPDATE from OP: SOLVED. Just hooked up my new Roku 4… all problems fixed. The past few days it seemed the problem was intermittent, or changing, as some others have posted. I’d suspected that minor variations in signal strength/quality from the antenna may have been involved. After finally getting a few hours to totally trouble shoot this here’s my best guess:
Yes, I was having intermittent signal issues from the antenna. Once the ground thaws I’ll move the antenna to a better location. And yes, the Chromecast was a big part of my problem. So whenever there was a drop in signal, no matter how small or how brief, Tablo would buffer… I think because the chromecast was having trouble decoding that signal since it didn’t meet the signal quality specs that Tablo and CC needed. Alos, and I think this is a major factor in the solution, my android phone was getting tablo’s signal via wifi, then casting and sending it back to the CC. A lot of unnecessary steps, using relatively slow wifi (my router’s pretty old… it’s G).

Now, with Roku 4 those wifi paths aren’t needed. Plus, the Tablo app in Roku is pretty darn fast, less time to start watching, fast forwading is a breeze, etc. So in layman’s terms, now the video signal comes from the internet thru my router, hardwired to Roku, hardwired to TV via HDMI. And for Tablo, it’s hardwired too so the signal goes from Tablo, to router, and then Roku picks it up from there. All wired.

I just did some recording tests… max quality is perfect, so my old router seems to handle it fine. I guess if I had a new router using the AC technology maybe that would be fast enough to negate the need for hardwiring, but in my case it is currently not absolutely necessary, and as a TV Producer/Director, I know that hardwires are always a good thing.

I was also really impressed with the channels on Roku. No, I’m not a shill for Roku or anything like that, I’m jsut happy this solved my issue.
My next, and hopefully final step, is to get Dolby Digital 5.1 working thru the Roku. The optical out was a nice feature on the Roku 4, but it’s not totally necessary… since I have an old AVR without HMDMI inputs, I could buy a cheap $60 box that strips out the 5.1 from HDMI outputting it to optical, while still passing HDMI on to TV. From what I’ve gathered, that probably won’t be a fix though, apparantely the main issue is the streamers like Netflix are sending DD+ only, not DD 5.1, and optical can’t handle the bandwidth for DD+, only HDMI. I wish some would make a dobly conversion box that takes DD+ and downconverts it to 5.1, outputting to optical. If anyone knows of one please let me know.