Tom,

Yes to the dewaxer and degreaser first, however, the 320 and the 400 will be a bit to agressive to just sand off the flaking clear coat. Instead I suggest some 600 grit, wet dry is best, but if not, then dry will have to do. Use a block sander instead of a DA, as you'll have a better chance to monitor your work and not burn through the base.

Of course with that said, do you know if your truck is painted base/clear, or perhaps a single stage enamel with clear shot over it, as this too will affect how you can handle, or man handle the flaking clear coat.

Will await your detailed response and perhaps a detailed digital picture or two and we'll take it from there.

Bill S.