1) When you created the graphic in Photoshop did you set the image frame size of the psd fileto be the same as the frame size in your video project – eg. 1920 x 1080 pixels for HD?
2) Did you create the graphic at it’s final size within Photoshop, or did you resize it in Avid? I never resize in Avid, and always create the final size I want in Photoshop.
3) Did you leave the graphic images as vectors in Photoshop? If you rasterized them that could make them look less sharp.
I create all my graphics and lower thirds in Photoshop and never have any problems with them in Avid.