Default [Q] Stuttering video N10 + portable HDD + Nexus Media Importer

I am not rooted and cannot because some of my apps require non-root (DirecTv) which makes me sad.

I just want to watch movies on my tablet. I have Nexus Media Importer (NMI) and I can see my Western Digital 1TB portable HD (formatted NTFS). And I can sort of play the movies on the drive using NMI & MX Player. I say "sort of" because some time after starting the movie there's stuttering and freezes. The Hard drive is model WDBZFP0010BBK - 05 which is actually a USB 3.0 drive, but works fine with just USB 2.0 cables. I've got it hooked up to my computer right now with just a micro USB cable and no other power.

Most of my movies are MKV, but some are MP4 and AVI. So far I haven't been able to play any of them. Some of them are upwards of 8GB, but some are only like 750MB. Again, nothing plays all the way through. They all start off like all is well, but eventually, pauses, stutters, hiccups, etc.

I have AVS converter and I could convert them to some other format, if that seemed like it would help.

Any suggestions? Is is my hard drive? Cables? Media format? Sunspots?