Resolution issues on WD15 Dock with three monitors

I have a Precision 5510 Laptop with Windows 10 and a WD15 dock (type-C). All drivers/BIOS/dock firmware were updated as of 4/12/17.

Intel Graphics 530 driver version: 21.20.16.4590

I have 3 Dell monitors connected as follows:

Monitor 1  (Dell 2314H) connected via DVI to dock mini-display adapter (1920 x 1080)
Monitor 2 (Dell 2314H)connected via DVI to the HDMI adapter (1920 x 1080)
Monitor 3 via VGA cable to the dock (640 x 480)

For monitor 3, I have tried 2 different models -

Dell S2330MX-  - capable of 1920 x 1080 at 60Hz

Dell S2340M - capable of 1920 x 1080 at 60Hz

Monitor 1 is the primary and the desktop is extended to use all 3 while the 5510 is closed, I cannot get the resolution on monitor 3 to go any higher than the 640 x 480.
Documentation Provided by Dell-Robert p over at http://en.community.dell.com/support-forums/laptop/f/3519/t/20004811

suggests that I should be able to get 3x 1280x 1024

Any help would be appreciated!!