It’s also possible, depending on your sequence settings, to have TOO MUCH resolution on your stills. If the stills are very high resolution, try reducing them down in PhotoShop to a size more in line with your sequence settings. If you don’t need to do moves on the stills, make them the closest size to your project settings. If they look all “crawly”, you can try adding a very slight blur to the stills to take the edge off of them.
E=MC2+/-2db