Originally Posted by
pixelstick
At that point I realized that the shifter wasn't pulling the cable and after spending so much time routing the cable I just took it to the LBS, which is where they saw the problem.
In your original description (and here as well) you state that "shifter wasn't pulling the cable". This is, of course, a completely different problem, which has nothing to do with double-crossed cables in the downtube. At the same time, you said that bicycle shop later had to deal with double-crossed cables in the downtube. So, we are observing two different unrelated problems here:
1) "shifter not pulling the cable" (apparently, your original mistake),
2) "double-crossed cables in the downtube" (apparently introduced by an incompetent mechanic while trying to fix problem 1)
So, what what the reason for the original problem?