It could be a DirectX issue. I ran into the same problem as you have described. And I switched to launch in Rage with DirectX 10 instead of 11 and it worked for me. Give it a try and let me know if you have success doing that.
West Coast Wookie, what can I say, this is an amazing vehicle and livery. It is now my go to Sherriffs unit. Thanks to Benzo Effect I found this. The ELS is off the hook. So 5 out of 5 stars will be my rating for this truck. Love to try more of your vehicles. I'm new to LSPDFR so I don't have much experience yet, but this truck gives my game so much more immersion. Keep up the good work.