Great Preview Playback / Very Slow Lagfull Timeline Playback
I have always used PP 2015 (just updated to the cloud a week or so ago) My is when I first updated to PP 2018 was that I could preview clips with no lag at all but the moment I crop (in point out point) them and drop them in the timeline and play it back (space bar) I get the most annoying lag. So much so I basically have to scrub through and hope for the best. The video play back is very choppy while the audio plays smoothly
I figured it was my system causing the problem (27-inch, late 2013 iMac, 8G ram, 1 TB HD, 3.5 GHz Intel Core) so I maxed the (32) Ram and swapped the internal HD for 1TB SSD and cleaned out all unwanted data (cleared my cache). After all of this nothing changed. I still get buttery smooth playback when simply previewing footage in the preview window (top left) But as soon as I drop anything to my timeline (top right) I get constant lag. (I'm so eager to edit using 2 timelines its the reason I finally ungraded).
I uploaded a quick one minute video showcasing my experience while preparing to edit a kids party recap video. You can see me watch a preview with ease then jump into lag lang which is my Selects timeline.
Note: when I check the activity monitor the %CPU dances between 120 - 377(max) for both actions
footage: Sony A7s ii (4k 24fps, 1080 125fps)
iMac (27-inch, Late 2013)
Processor: 3.2Ghz Intel Core i5
RAM: 32GB
Graphics Card: NVIDIA GeForce GT 755M 1GB
OS: High Sierra (10.13.2)
Can anyone help me with this issue? i would be greatly appreciated. Thanks
PS: If this has been asked and answered feel free to point me in the write direction.

