Diet Cokes are my friend and enemy...Mountain Dew has the highest content of caffeine of any soft drink other than those Red Bull varieties...
Sadly, this isn't true in Canada, here Mountain Dew has no caffeine at all. I believe we have some type of restriction that caffeinated soft drinks have to be coke-coloured, not clear. This might actually be helpful for the OP, if he can get Canadian Mountain Dew, it might help reduce the number of changes his body has to adjust to at the same time