Here is the problem, sonyvegas used to be working fine with my R9 280x. After I upgraded by PC with an GTX 1060 I get this problem. The video in preview is smooth butlaggs for a couple seconds or sometimes freezes when going over a split.
Example: https://gyazo.com/76060dbed1e9fb550fb8335c34606600
My PC specs:
i5 4460
gtx 1060
8gb ram
video's are on an external hard disk but this isn't a problem
sonyvegas pro14