Go to http://www.natgeomaps.com/downloads.html
and note the link that offers TOPO! Version 3.4.3 as a free upgrade for TOPO State Series users running versions 2.6 or higher. (assuming what you have is a state series). They also offer an "upgrade kit" to version 4.5 for $20, but I suggest that you try the free upgrade and see if that provides the functionality that you're looking for.
Warning, however: in my limited experience, it seems like some upgrades along the way added new bugs when they fixed old ones (and added features). I generally found ways around problems, however, so given that there's specific functionality that you want, and that you can be sure that in some later version it's provided ... I'd be inclined to upgrade and give it a try. At worst I would expect you could always un-install and then reinstall your older version.