Multiple Trucks Parked Lag

[78TruexFan]

So I have been trying to get 12-14 trucks in a stadium. I can actually get all 14 without any FPS drop. But when I freestyle I start out around 60 FPS but then drop to 20 or less like mid way through the run. This also happens when I even have 8 trucks in a track. Is there a way to fix FPS drops. I understand I have a lot of trucks on the track at once but I have a VERY great pc. 
 

GPU - 2070

CPU - AMD Ryxen 9 

Ram - 48 GB

 

So in conclusion is there say solution to this? On my old pc I was able to do all 14 without really any problem. With that said it was like a year ago I did this. So I may have forgotten any tips that I had learned. I hope this all makes sense.