Premiere Pro CC (2018 v 12.0.0) Massive playback issue - Reinstalling 2017

Premiere CC 2018 v12.0.0 (downloaded / installed last night)

Issue: Limited video playback in Program viewer, 10 or 15 secs playback on average and then just audio would continue.
System: iMac (late 2013) 3.5 GHz Intel Core i7, 16 GB memory

Is anyone else having this issue?

To Whom It may Concern (Adobe Community, Support & Engineering),

I suppose I was too optimistic downloading a new "upgrade" version and expecting it to somehow have better performance.

I just lost hours of time and maybe 1/2 hour of progress editing, finishing a project, working with multiple deadlines. No time for this, folks.
Tried deleting cache, rendering workspace, playing 50% frame size at 1/2 resolution, etc etc, no difference.
Uninstalled 2018, reinstalled 2017. Letting it go, moving forward. If I had time I would also check sequence settings for Preview file format rendering, put on i Frame only MPEG if it wasn't on that...in fact - I'll take another 30+ min to do that, closing 2017, re-installing 2018 again....opening project with latest work with playback issues...support was really helpful last November 2017 when endless crashes were finally circumvented by changing that Preview format codec.....Preview file codec was / is on i frame only MPEG, so I just unchecked Max bit depth, render quality and Linear color composite options, also switched Editing Mode codec toggle to AVC-Intra 100 1080p from ARRI cinema, I think either of them worked best with I-Frame Only MPEG Preview (editing with video from Canon 5DM2 as primary source camera. Also using lots of high res jpegs exported from Lightroom and graphics from After effects rendered out at AppleProRes 422 HQ).

Ok, keeping fingers crossed with re-install and new Preview rendered playback of 30 secs of sequence...voila, it's not hanging or stuttering at all - yay.

Hope this might have helped someone. Thanks to all the creatives and engineers. Keep pluggin.

Back to it,
FB