Assigning Specific ID's to Posts?

Pretty sure wordpress does that on its own, why do you want to do this? We may be able to find a different solution.

The post table, and thus Post IDs, are used for a myriad of other things including Pages, attachments, revisions, menus, and custom posts types, so you can’t control the assignment of Post IDs.

You could create a Custom Field and use that to assign your own ID.

I am using Agentpress theme and some third party tools for the slideshow, don’t know how I can make a better use of the Custom Field?

But what are you trying to achieve?