there's a lot beyond disk read speed that goes into how media plays in premiere and without more info there's no way we can even guess what's going on. Please tell us your system specs: OS version, Premiere version, amount of RAM, Hardware specs including graphics card and your source properties and sequence settings. And just because a drive has an advertised read speed, doesn't mean it actually will work that well. You might find a drive speed utility and see what the read and write speed for the drive actually are. I have something on my system called AJA System Test Lite. You might google and see if it's still available. AJA's a reputable company... and I think it was free.