You can insert an URL hyperlink to another post by inserting the post's URL into the text. I suggest using the URL tool that facilitates adding a title.
Additionally, moderators can create a 'shortcut' for a post which places the same post in multiple forums. This is done when the post has a proper fit in more than one area.
'11 GMC Acadia SLT AWD
'11 GMC Sierra 1500 4x4 Extended Cab