Installation:

1: Install this mod:
https://www.gta5-mods.com/vehicles/maibatsu-mule-4x4-addon 

2: Extract the "nmule_sign_28.dds" file.

3 Using OpenIV, access "D:\SteamLibrary\steamapps\common\Grand Theft Auto V\mods\update\x64\dlcpacks\nmule\dlc.rpf\x64\vehicles.rpf\"

4: Add the "nmule_sign_28.dds" file to "nmule.ytd" and nmule+hi.ytd"

Credit for the Maibatsu Mule 4x4 goes to Dani02