I was told that this could be a handling or vehicles.ide issue, I backed them both up and used them. Sometimes it's fine in game, but it's usually not. The same thing is happening to my ambulance too. Any ideas as to what's causing it?

 

 

too high polygon count i think, or it's got with the handling 

Which handling lines did you use?

 

Polygon count is only 50,000, I have used much more high-poly vehicles before and never had this problem. I am using the vanilla handling line, I have never experienced this issue before. Could it be my game or the model? If you want, I could post it....

I had a similar problem with some of Yard1's vanilla models after I installed too many skins on them. Maybe that's the problem?

The .WTD file seems a bit heavy on both, it's around 3-4 MB.

It's the model it self.

Its normally the result of too many "misc" parts going together with a lot of extras that cause it. The problem is with the models, there's nothing you can do about it. It'd be best if you report the bugs to the person(s) that released the mods so that they can fix them.