This gearbox mod is for the Volvo FH16 truck.
This gearbox’s ratio such as an older diesel car’s.
I mean the rpm like in the cars:

500 rpm = 1000 rpm (in car)
1000 rpm = 2000 rpm (-II-)
1500 rpm = 3000 rpm (-II-)
2000 rpm = 4000 rpm (-II-)
2500 rpm = 5000 rpm (-II-)
3000 rpm = 6000 rpm (-II-)

So the truck with this can run more than 180 km/h. This mod recommended with 750 hp engine. The high speed with 750 hp engine is 185-186 km/h.
I suggest to install 1000 or more hp engine mods. Then it runs at 230-240 km/h.
This mod tested in version 1.33.2.19.

Credits:
anonymous