The total URLs on my sitemap is 2.5k but google only manages to index half of that. All my older posts are getting indexed but the newer half aren't getting in at all and its been a while already, does it just need more time or is there something wrong? Thanks
If they are just having unique content and you have posted them too earlier then wait more till google crawl them next
Check that you not duplicating titles or meta descriptions, google can ignore them if there the same. If thats fine, try setting the priority index to high on some of the new urls and see if google still ignores them.
Give it some time. Sitemaps doesn't have anything related how many pages will appear in SER (search engines results). It's only informational and directional to Google (great thing for Ajax pages cause they are hard to discover for search engines). After all, big G is deciding which one of them will appear in index. Read their's FAQ page and you'll know everything.