Ok, so i was attempting to follow an online Tutorial for retexturing... got the new texture onto the armor and into game but after 10 minutes of running around i just realized this!
Are you sure it's only happening with that one piece of armor? I've had that happen to me a couple of times with content in the vanilla game; not sure what triggers it. For me, unequipping the armor, saving the game, exiting new Vegas, reloading, and re-equipping the armor fixed the issue.
This is not likely a texture/alpha issue, if it were the break wouldn't be so clean (unless it was specifically designed for that purpose by aligning the UV map edges vertically so a non-aliased alpha could be made for it). It'll most likely be related to the section of the model that's not rendered when you're wearing PipBoy somehow in any case, though I don't know how that's handled.
Edit: Correction. If that section of the model has a separate UV shell, you COULD get that effect with an unintentional alpha. It's still probably related to the PipBoy though, take it off and see if it goes away.
well, downloaded the readius pipboy mod. removes the pipboy from your arm and give a new menu design layout. Fixed the issue. Thanks for the suggestions all