Requirements: 

Marias Pass: https://store.steampowered.com/app/222561/Train_Simulator_Marias_Pass_Route_AddOn/

(Optional) ShermanHill: https://store.steampowered.com/app/208286/Train_Simulator_Sherman_Hill_Route_AddOn/

MLWAudio GEVO-12 Enhancement Pack

Step 1: Copy the Assets folder and paste it into C:\Program Files (x86)\Steam\steamapps\common\RailWorks 

Step 2: Copy ES44DC_BNSF.GeoPxDx from C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\RSC\MariasPass\RailVehicles\Diesel\ES44DC\BNSF\Engine
and paste it into C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\RSC\MariasPass\RailVehicles\Diesel\ES44DC\UP_C45AH\Engine

Step 3: Copy es44dc_cab.GeoPcDX from C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\RSC\MariasPass\RailVehicles\Diesel\ES44DC\BNSF\CabView
and paste it into C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\RSC\MariasPass\RailVehicles\Diesel\ES44DC\UP_C45AH\CabView

Step 4: Repeat the process for the T4C Unit

(Optional) Step 5: Copy the ShermanHill Folder located in the download

(Optional) Step 6: Paste into your Mail RailWorks - Assets Folder

That's it! Enjoy your new UP GEVOs & Textured Enhanced ShermanHill Unit! :)