Just found this replacement product today where the Throwback used to be. After checking the label to make sure no artificial sweeteners had snuck in there, I bought exactly one 2 liter bottle to check it out. Haven't opened it yet, but checked online to see what was what. As of June of this year, Pepsi is replacing the Throwback product in many areas with Pepsi with Real Sugar - very similar labeling to regular Pepsi.
Pepsi has changed the formula by reducing the sodium count, and increasing potassium content; the calorie count and the recipe remain substantially the same time. However they did tweak it, so it isn't strictly speaking the 70s-80s formula that we are used to.
Throwback: 40 mg Sodium per 12 oz. Serving; 0 mg Potassium
Real Sugar: 30 mg Sodium per 12 oz. Serving; 10 mg Potassium
They're also reducing the sugar in their 20 oz. Bottles to bring the calorie count down to 250, from the previous 260. (I haven't seen PTB in 20 oz. Bottles since they introduced the product!)
I still have Throwback in-house; as soon as I can properly chill the new product, I'll do my own (not blind) side-by-side comparison.