Found a list of possible flavorings in dr pepper.
cola
cherry
licorice
amaretto (almond)
vanilla (vanillin)
blackberry
apricot
caramel
pepper
anise
sarsparilla
ginger
molasses
lemon
plum (prune)
orange
nutmeg
cardamon
all spice
coriander
juniper
birch
and prickly ash
the company denies most of those (cola,plum,pepper)
I have heard adding amaretto to cola can come close.
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the Cola Syrup is a little sweeter and has a slightly different flavor profile. Wizard labs carries mostly TFA flavors, $1.50 for 8ml, try 'em both...