Playback is awful at 1/4 res.. no effects with Premiere cc 2017 on a late 2013 Macbook pro? Help

the machine:

 

macbook pro (retina, 15-inch, late 2013) running el capitan

 

2.3 ghz intel core i7

 

16 gb 1600 mhz ddr3

 

nvidia geforce gt 750m 2048 mb

 

playback off external thunderbolt drive.

 

media gh4

mostly:

type: mpeg movie

file size: 6.24 mb

image size: 1920 x 1080

frame rate: 23.976

source audio format: 48000 hz - 16 bit - stereo

project audio format: 48000 hz - 32 bit floating point - stereo

total duration: 00:00:01:00

pixel aspect ratio: 1.0

vr projection: none

 

since upgraded premiere 2017, can't sustained playback anymore, , machine should handle @ 1.4 resolution un effected footage 

i'm wondering if premiere has done leave hardware behind upgrade.  can't work this.

 

i've tried toggling between cuda , opencl , same problem.   cpu fan screaming @ me, , playback stuttered after few seconds.

 

i can see in activity monitor minute touch thumbnail or timeline i'm @ 500 plus per cent of cpu usage.

 

any suggestions?

have tried video on internal drive?

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