emptw1

Do you have every other vehicle modded? (All police vehicles and the Ambulance and Fire Truck). If so, try Making one of the other vehicles a vanilla, and then have the polpatriot with a modded ELS vehicle (I know that having all ELS vehicles can make the game unstable, and by just having 1 vanilla can increase stability)
It could also be to do with the polys of the vehicles you're using, and your computer can't handle it, try using a modded non ELS vehicle, they tend to have less polys.
It could just be that those models don't work on your computer. I know that for me, a GMC Yukon won't work 9/10 of the times I use it, so, try as many vehicles as you can (even cars like the Taurus or Crown Victoria) and see how that goes.