Possibly an authoritative source on redding up's origins comes to us from commenter Beau:
Interestingly, I found a Pittsburgh winery that makes a Redd-Up Redd wine, adding even more credence to the claim that this hails from that area. And, look, there's a Redd Up Pittsburgh T-shirt.
And, if you want a real authoritative source, how can you get more credible than PBS?
All right, I promise I'm done talking about redding up for a while.
Nope, we're not quit finished with redd-up. I was born in Juniata Co.--45 mins. n. of H'burg--and learned to speak Pennsyltuckian back then as a child. Today, I'm as old as dirt so it's been a while. Now, considering that PA was settled from east to west, considering that PBS & others give the Scotch-Irish the credit for some of our colloquialisms, how can Pittsburgers make such a claim as Beau has done when civilization reached Pittsburg last? Sorry, P'burgers, you guys came too late in the game for that claim to be credible.