Encoding is slow

I posted this in another section of the forum but was told to re post it here in the hopes this may be a hardware problem.  I've done Bill's PPBM8 test, the results are below.

PPBM8 Results: 56/45/14/185

I've just built a new system with speed in mind, specks are below.  I'm trying to export a video out of Premiere, it's 4K video shot at 60 FPS that's being saved out to 1080P@59.94 FPS and the entire clip is about 1.2 minutes long.  The clip is made up of two nested sequences, the first is a two layer comp, one layer is regular 4K video and the second layer is an animation sequence with an alpha channel, the second nested sequence is a linked after effects comp.  I'm saving out the video using the H.264 format & the high quality 1080p preset, render at maximum depth is checked as well as use maximum render quality, all other settings are default.   The time it's taking to encode this video is in excess of an hour and if my machine were maxed out I would be ok with that but it isn't.  During the encoding process CPU usage never gets above 2% and sometimes sits at 0% for many seconds, it's the same for the GPU, memory usage is about 19GB out of 128GB.  I'm at a loss to explain this and I can't see any way to speed up the process, I'd really appreciate some insight and help with this, is there no way to speed up encoding?  

-Windows 10 Pro

-Xeon Gold 6146@3.20 Ghz x2

-128 GB Ram

-2 TB SSD

-Nvidia Quadro P6000