ID5.5 image dpi cut from 300 to 150 in save as ps, acrobat to pdf

When I submitted book interior to printer, they said some images were 150 dpi. I checked the ID file links, and they showed them as 300 dpi. My process to pdf was: from ID, save as postscript file, then use Acrobat Pro with the PDFx1a2001 profile to create the pdf. Any thoughts on where in this process the images would be downgraded to 150 dpi? Here is the file as ID shows it:

Thanks for any suggestions.