Hi

The main difference between MEP 2016 and 17 is that 2016 is a 64 bit program, which means it can use more memory and can perform some operations faster than the 32 bit versions.

What I suspect has happened with your computer is that the switch to 64 bit has tipped your computer over the edge with respect to achieving smooth playback especially if you are not using proxy files and Hardware acceleration and have the Preview monitor set to use Reduced resolution, Reduced framerate

Proxy files have two uses -

    they give smoother preview playback on lower specification computers when working with HD video
    
    they can be used for export or DVD creation - this gives a signiicant speed increase in rendering the video particularly if the source video is HD.

The option to use proxy files is in the Projects settings ( E key)

Hardware acceleration (HWA) improves playback performance and depending on the fades and effects you have used they may not use hardware acceleration to render them during preview - crossfades, colour fades and some 3D transitions are hardware accelerated, many other effects, eg blinds, are not hardware accelerated.

The option to turn on HWA is in the programs settings ( Y key)

Preview monitor performance - Reduced resolution, Reduced framerate.

Right click the lightning symbol bottom right of the preview monitor to see and set these options.

Note: there are times when the above do not help - these are usually when very complex arrangements are on the timeline.

HTH

John EB