Olipcs is correct. If you want a program to receive an uppercase E you need to use SendWinS for that character. (You can make a second label for that purpose.) Just because WoW receives a Shift and then receives an E doesn't necessarily mean WoW will interpret the E as uppercase. Background keystroke injection is more complicated than that.

Anhvariel, what "mouse button modifier keys" are you talking about? The only modifier I see in your script is Shift.

And when you say Shift 1 or Shift E isn't getting received, how are you judging that? What bindings in the game are you expecting Shift 1 and Shift E to trigger?