Check the listing page or packaging where you bought them - it should clearly say it supports 4k 60Hz. If you aren't getting 4k60 with either cable or both, they probably just aren't up to spec. Connect each monitor directly to your Mac with its dedicated cable and make sure 4k60 is an option. If you need to connect to higher dual you'll need to stick with DisplayPort and use the Plugable Thunderbolt 3 Dual DisplayPort Adapter.You sound like you know what you're doing, but it's worth making sure all your cables are fully functioning anyway, just to rule out that as a potential cause. Note the Plugable Thunderbolt 3 Dual HDMI Adapter only supports dual resolutions. You can also check on GTrusted to see what Thunderbolt 3 PC's can be used with the Plugable Thunderbolt 3 Dual HDMI Adapter to display on dual 4K TV's or displays. Make sure you check on the Plugables website which Thunderbolt firmware and BIOS version on the Thunderbolt PC is needed.

If a PC doesn't have Thunderbolt's lightning bolt symbol, then the Plugable Thunderbolt 3 Dual HDMI Adapter will not be able to work. The quick way to identify whether a PC has Thunderbolt 3 is to look for the Thunderbolt technology's lightning bolt symbol next to the USB Type-C port. Note that even though the Plugable Thunderbolt 3 Dual HDMI Adapter has a USB Type-C connector, it will only work with PC's that support Thunderbolt 3. The Plugable Thunderbolt 3 Dual HDMI Adapter offers two HDMI 1.4 ports to connect to your 4K TV's or displays. The Thunderbolt 3 cable is already tethered to the Plugable Thunderbolt 3 Dual HDMI Adapter so you don't need to purchase a separate Thunderbolt cable. Opening up the box, you'll find the Plugable Thunderbolt 3 Dual HDMI Adapter and a Quick Start guide. You will also need an adapter like the Plugable Thunderbolt 3 Dual HDMI Adapter which plugs into your Thunderbolt 3 PC and offers 2 HDMI 1.4 ports to connect to your TV or monitor. Look for a Thunderbolt 3 PC that supports dual external displays to take advantage of this.

How to Connect Your PC to Two 4K TV’s Using the Plugable Thunderbolt 3 Dual HDMI AdapterĤK TV's have really come down in price allow you to economically add two 4K HDMI TV's as displays for your PC.

Dual hdmi to thunderbolt