The invention is a shift lockout guide for a vehicle equipped with a manual gearbox. It includes a user-operable means that, in preferred embodiments, is mounted to the shifter of the gear box and is linked to an engagement portion that interacts with guide plates defining a path of travel for the shifter. A biasing means urges the engagement portion into the guide plates but this can be overridden by the driver through the user-operable means. The invention provides the driver of a vehicle fitted with the invention in the selection of specific gears while also preventing certain other gears from being selected. This reduces the risk of inadvertent overrevving of the vehicle's engine through inappropriate gear selection.

A compression brake control shifter for convenient and safe compression brake control from the shifter includes a shifter body. The shifter body is configured to connect to a shift lever of a truck to manipulate a gear system of the truck. The truck has a gear splitter and a compression brake. A wiring harness is coupled to the shifter body and extends through the bottom side to be in operational communication with a CPU of the truck. A compression button, a hi/low gears switch, and a gear splitter switch are coupled to the shifter body and are in operational communication with the wiring harness to activate and alternatively deactivate the compression brake of the truck, to switch to and from a hi gear mode and a low gear mode of the gear system, and to activate and alternatively deactivate the gear splitter of the truck, respectively.