The video files that I take with my Iphone. About 1/4-1/3 of videos I work with are off my Iphone. On my desktop there is no lag in preview when I use Pro 16, but there is when I use my newly purchased Pro18, kinda frustrating.

That was actually a hint.

Kindly click the link I provided and post your required Vegas and MediaInfo file properties, many thanks.

Welcome to the forums.

I am no expert on this, but most smart phone videos have a variable frame rate (VFR).. which Vegas does not like. Many folks here use HandBrake or HOS to transcode to (constant) CFR

I am not that tech savvy myself, I have all I can do to just learn the features of Vegas and be able to comfortably use many of them for my editing. I think my desk top computer is powerful enough, but what frustrates me the most is that I don't have this problem with VP16, so for the time being I will continue to use VP 16 for editing those videos. I very much appreciate everyone's comments to help me get VP 18 up to speed, I certainly will listen to everyone's comments and go from there. Maybe sometime later a VP 18 upgrade will help?

Thank you for sharing. You don't need to be tech savvy to follow the instructions. If you're not comfortable posting your file details, the best anyone can do is guess at your problem. @rraud's reply is a good place to start, ang good luck.

"Maybe sometime later a VP 18 upgrade will help?"

Not likely, these issues have been ongoing for years. Start with @Musicvid and @rraud's suggestions

I really appreciate everyone's comments in helping me out with this issue. Later tonight or tomorrow when I have some more time I will dive into this and see if I can resolve it, or at least get further along. Again, I appreciate everyone taking the time, very much appreciated.