This sounds like it should be in Technical Support
Also please fill out the Support Template so we have all the information about your system, System Specifications (Graphics Card type and amount of graphics memory, would be helpful).
The flickering is a known issue in the engine, but a heavy texture load can make it much worse.
Try a basic server with vanilla GTA, rather than ones with crazy “mod” vehicles which often have ridiculous textures and see if it is better.
Turning off AA may help, if you have an NVidia card check out their Guide for GTA V