So I got a response from Sprint e-care. They put me through to advanced device tech support.
(I was surprised such a simple question required advanced support.) Nobody I spoke with has any knowledge of there being a newer version of Sprint Navigation for the Touch Pro than version 2.1. They are not saying anything about using Telenav minus their branding either. The person I spoke with in advanced support, once I mentioned that Telenav said there is a 3.6 version of Sprint Navigation, started looking to see if they could find it. Then they said
"I'm on google.com searching for it", which almost made me laugh out loud! I'm not sure why Sprint does not have an answer for a question like this handy. Finally, I was directed to
this page.
(I guess they do keep this sort of thing listed somewhere after all.) Which shows Sprint Navigation 2.1 is the latest Sprint claims to have available for the Touch Pro. The advanced support representative said they
"don't know" why Tenelav support said there is a 3.6 version of Sprint Navigation available for the Sprint Touch Pro.
So for now, Telenav 5.1.16 is as good as it gets for us.