This is the continuation of the mod More Realistic Gearbox Addon for LS13. In FS 2015 it works even without a More Realistic.
Not every tractor has a continuously variable transmission. This mod based on the configuration file zzzMrGearboxAddonConfig.xml the configured there tractors subsequently added a gear shift. Currently these tractors are already configured:

Deutz Agro Star 6.61
- 48 forward and 12 reverse gears
- 6 courses
- powershift speeds

Same Fortis 190
- 24 forward and 24 reverse gears
- 6 courses
- 4 powershift speeds with automatic
- Reverse Gear

Lindner Geotrac 94
- 16 forward and 8 reverse gears
- 4 courses
- 2 stages with automatic load scarf (speed matching)
- 2 groups + 1 reverse

Buehrer 6135A
- 15 forward and 3 reverse gears
- 3 groups
- Extended Final Reduction to 42 km / h

MAN TGS
- 12 forward and 2 reverse gears
- automatic

Case IH Quadtrac 620
- 16 forward and 2 reverse gears
- powershift
- automatic

Steyr 4115
- 32 forward and reverse gears
- 4 gears
- 4 powershift groups
- 2 groups (A and S)
- reverser

The operation is done using the following keys:
[ and ': shift up and down
;: neutral on/off
right shift plus ;: gear box on/off
] And #: group up/down, same with the right shift key for group 2
> and /: manual clutch, important when starting uphill
Spacebar: reversing gear forward / backward
right shift plus spacebar: automatic clutch on/off

Credits:
mogli aka biedens