I just bought x-plane from the x-plane.com website, downloaded it but the frame-rate is extremly low even though I have a 4 GHZ processor, 32- GB RAM and a SSD-drive....can't be used as a simulator, not even with a C172! - My grafic-card is a R9 Radion with 8 GB VRAM....why is X-Plane running so slow??