SMP wrote up a fairly complete doc of the issues he encountered in an article:
https://devcentral.f5.com/Tutorials/TechTips/tabid/63/articleType/ArticleView/articleId/1084376/Problems-Overcome-During-a-Major-LTM-SoftwareHardware-Upgrade.aspx
Here is the SOL on the monitor send string change:
sol10655: Change in Behavior: CR/LF characters appended to the HTTP monitor Send string
http://support.f5.com/kb/en-us/solutions/public/10000/600/sol10655.html
You can also get more info from the LTM and GTM release notes:
https://support.f5.com/kb/en-us/products/big-ip_ltm/releasenotes/product/relnotes-LTM-10-2-3.html
https://support.f5.com/kb/en-us/products/big-ip_gtm/releasenotes/product/relnotes-GTM-10-2-3.html
I suggest contacting your F5 or partner SE for help in planning the upgrade.
Aaron