I recently purchased an Alienware Aurora R6 with an AMD RX480 8GB card installed.  I have 2 Dell U2515H monitors, both normally running at 2560 X 1440.  The displayport on my card can support the full resolution just fine, but the other monitor connected to the HDMI port can only go up to 2048 X 1152.

When I connect both monitors to a much older AMD card installed in my 3-year-old Dell OptiPlex machine, they both work fine at the full resolution.

I have installed the latest AMD video drivers, but no luck.  I know that the HDMI port on this card is supposed to support even 4K resolutions, so this does not make sense.  I do not have a DP to HDMI cable that I can use to test, so that I could use one of the other DP ports on the card instead, but I'll buy one if this is the only way to get it to work.

Has anybody else encountered this problem?