iMac (Retina 5K, 27-inch, Late 2015) 3.2 GHz Quad-Core Intel Core i5 32 GB 1867 MHz DDR3 AMD Radeon R9 M390 2 GB The 11.5.1 update caused video/trackpad stuttering. I also lost my directly-connected Dell monitor (iMac thunderbolt to Dell DisplayPort) video. Turning off the Dell fixed the stuttering. Moving the thunderbolt connection from the iMac to my CalDigit hub fixed the second monitor issue. Is it possible to update or reset the iMac's thunderbolt port? I've reset the PRAM so far...   Vendor Name: Apple Inc.   Device Name: iMac   UID: 0x0001001901E3F1E0   Route String: 0   Firmware Version: 28.1   Domain UUID: 3D365C05-5471-5A50-BA61-960AEA98039C   Port:   Status: Device connected   Link Status: 0x2   Speed: Up to 20 Gb/s x1   Current Link Width: 0x2   Receptacle: 1   Cable Firmware Version: 0.1.22   Link Controller Firmware Version: 0.16.0

iMac (Retina 5K, 27-inch, Late 2015) 3.2 GHz Quad-Core Intel Core i5 32 GB 1867 MHz DDR3 AMD Radeon R9 M390 2 GB The 11.5.1 update caused video/trackpad stuttering. I also lost my directly-connected Dell monitor (iMac thunderbolt to Dell DisplayPort) video. Turning off the Dell fixed the stuttering. Moving the thunderbolt connection from the iMac to my CalDigit hub fixed the second monitor issue. Is it possible to update or reset the iMac's thunderbolt port? I've reset the PRAM so far... ` Vendor Name: Apple Inc.   Device Name: iMac   UID: 0x0001001901E3F1E0   Route String: 0   Firmware Version: 28.1   Domain UUID: 3D365C05-5471-5A50-BA61-960AEA98039C   Port:   Status: Device connected   Link Status: 0x2   Speed: Up to 20 Gb/s x1   Current Link Width: 0x2   Receptacle: 1   Cable Firmware Version: 0.1.22   Link Controller Firmware Version: 0.16.0 `