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I suspected that those related products being marked up might not have been good. Good to know. We'll for sure test that out. Thanks for the recommendation on the blog post and for your help!

Check to see if they are both in the index (or 1 is in supplemental index). If so, it's an issue. In general, capitalization does mean a different url (think of all of the link shorteners that user a mix or upper and lower case letters in order to differentiate)

Update all internal links to point to the new URLs.  301 redirects don't pass 100% of the link juice. The best option is to create a 301 redirect rule(s) that handle all possible situations.  If that's not practical, then just worry about the ones that are linked to by external websites.  You can spot these by making the transition to the new URLs, then watching for 404 errors in Webmaster Tools, and looking for pages linked to by external sites. If you're using IIS, you can actually do some pretty complex logic in your 404 handler and make it return a 301 in certain cases.  Check this post I did a while back.

You might not have enough linkjuice into those pages to assure constant spidering.... and as a result, Google forgets those pages between crawls.