PC Lag And Performance Drops

I've said this before, but I play train sim world on a 2018 Razer Blade 15 with 60hz, 1080p, GeForce GTX 1060 Max-q, Intel i7-8750H, and 16gb RAM, which should be more than enough to run Train Sim World 2. The game is installed on me E: drive, a Seagate Portable HDD with 4.45 TB. However, I'll be playing at a smooth 45-60 FPS, but then my CPU will slowdown, and my framerate will drop to below 20. I have tried everything I could find online, and none of it worked. Can someone Please help me?

 

I suspect you may have a bottleneck in data transfer speeds to and from the portable HDD. Have you tried installing the game on an internal drive?