Explicitly Set Physx Processor

Some issues have been seen when the PhysX processor is set to Auto-select. This is most common on laptops.
1. Right click on your desktop and select NVIDIA Control Panel.

2. Go to Configure Surround, PhysX on the left.

3. In the circled dropdown on the right side select your graphics card.

Uninstall NVIDIA GeForce Experience

GeForce Experience is a companion app that provides some additional features in some cases, but can also introduce an additional source of issues. 
1. Open the start menu and type Add or Remove Programs, then select the app it suggests.

2. Find NVIDIA GeForce Experience in the list and follow the instructions to remove it.

Turn off Vertical sync

1.Right click on your desktop and select NVIDIA Control Panel.

2. Go to Manage 3Dsettings in the 3D settings section

3. On the Global Settings tab, turn off Vertical sync

4. And/or in the Program Settings tab, choose iRacing Motorsport Simulator and turn off Vertical sync
Disable Multiplane Overlay

Multiplane Overlay (MPO) is a power saving feature that can increase single screen performance, but is known to cause flickering and stuttering issues when used with G-SYNC. Nvidia provides registry files to disable and enable MPO.

1. Go to https://nvidia.custhelp.com/app/answers/detail/a_id/5157 and download "mpo_disable.reg"

2. Run "mpo_disable.reg"

3. Restart the computer