Which display engine are you using (Lightworks, RedSDK, GDI Native Draw) and which mode (Wireframe, Hidden Line, Draft Render, etc.)?
Also, which TurboCAD version?
Also, is this a recent change?
TC Pro Platinum 2019, 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1