Sony Vegas Pro 13 Lag


So i just got sony vegas 13 pro on my computer and threw some footage to edit in and it was going all good until i reached around the 20 minute mark. then the preview window started lagging to like 3 frames a second. my pc specs are
Intel i-7 6700K CPU
GeForce GTX 960
250 GB SSD
I thought this would be enough to run Vegas but i am still running into this lag problem. I looked up some solutions but none have worked yet. Any help would be appreciated. Thanks


my first thought would be at least another 8g ram


yeah i would suppose but if 4 GB is need for it to work and 8 is recommended i thought it should’ve worked fine with 8GB


agreed, with the system you have you should be fine but it isnt