One more test on the Torani Puremade Zero Sugar Caramel Syrup. Based it off of a cup of illy Extra Dark Roast and used 5 pumps instead of 4.
That did the trick.
The caramel flavor was there, the sweetness was there, everything I was looking for in a caramel syrup was there. No off tastes, no bitterness. I now recommend the syrup, although if your sweet tooth is like mine, you're going to burn through it quickly. Still, it *is* zero calories, so it might be worth $10 a bottle.