What other add-on are you using ? How's your fps ?
Vehicle position updates are driven by fps and, if you have too many other add-ons, especially those that send a lot of commands to the sim through Simconnect, they would all compete to get the sim attention, and this will be even worse if your fps is bad.
You can control this in GSX in some way, by checking the "Cap Simconnect udpates" in the Addon Manager. This settings forces GSX not to update with the frame rate, but at a fixed rate of 30 hz so, it won't spam the sim with too many request if your frame rate is higher than that.