how to add the mod download 
installe the zip folder and open the mod folder and select the (pounder.ytd and pounder+hi.ytd) and open (openiv) click to f6 and select yes and put him in ( mods/x64.rpf/levels/gta5/vehicles.rpf and search pounder and put the (pounder.ytd and pounder+hi.ytd) 
if you dont understand see this video 
enjoy!!!