The speed governor on the XRunner is set to 124 MPH. Most of the other trucks it is set to 105.
The reason the OEMs put speed governors on the vehicles is so you cannot exceed the maximum tire speed rating of the tires they install at the factory.
If you decide to raise the speed governor you must make sure the tires are properly rated for the speed you will be driving.
I have driven the URD XRunner to 170 MPH. This was accomplished using the URD Supercharger system with a raised engine RPM limit and removal of the vehicle speed governor. That was done with the discontinued X-1 engine controller. We have now switched to the UCON Flex Advanced Engine Controller from iTronix Technologies.
The engine in the URD XRunner is a stock engine with no internal mods other than the APR exhaust cam gears. We do have an engine being built. It was the first 1GR block to be sleeved by Darton. It has been at APR FOREVER now waiting on them to assemble it. Not much happening there. Might have to switch to plan B on that.
There is a video on our supercharger kit page of the truck with the older Mk2 supercharger system doing 150 MPH through a police RADAR trap in Tucson.
Since then we did the T-56 transmission swap and regeared the rear diff to 4.30 gears. You won't see it doing 170 MPH any more due to the much higher propeller shaft speed. Those Spicer made propeller shafts who also make the ones on the Turndra have a problem exploding on the Tundras when you remove the vehicle speed governor. So, until we have a custom drive shaft made, those super high speeds are no more.