Thanks, John.
I'm using Premiere Pro CS6, 6.0.3 on a Win 7 PC laptop.
My export settings are: PNG, 792x582 (same size as source). See the screencap image below for more Export settings info.
I've been exporting these with excellent results for the last week, and now the results are very poor, using the same settings.
My Preview File Format is the default I-frame only MPEG.
Renderer is the default Mercury Playback Engine.
Thanks...