Are you sure it's a Shift Key problem? Or is it just the \ and : keys?
If it's the \ and : keys, please read the DOSBox README.txt file, which is basically the User Guide.
New users please remember: DOSBox README.txt = DOSBox User Guide
Each chapter is short, it doesn't take long to read.
At the very least, read chapters 1 - 6 and 9 - 11.
1. Quickstart
2. FAQ
3. Usage (with Command Line options)
4. Internal Programs
5. Special Keys
6. Mapper
7. Keyboard Layout
8. Serial Multiplayer feature
9. How to run resource-demanding games
10. Troubleshooting
11. The config file
12. The language file
13. Building your own version of DOSBox
14. Special thanks
15. Contact
Reading Chapter 2. FAQ would reveal the following:
"Q: I can't type \ or : in DOSBox.
A: This is a known problem. It only occurs if your keyboard layout isn't US.
Some possible fixes:
1. Switch the keyboard layout of your operating system.
2. Use / instead.
3. Open dosbox.conf and change usescancodes=false to usescancodes=true.
4. Add the commands you want to execute to the "configfile".
5. Change the DOS keyboard layout (see Section 7 Keyboard Layout).
6. Use ALT-58 for : and ALT-92 for \.
7. for \ try the keys around "enter". For ":" try shift and the keys
between "enter" and "l" (US keyboard layout).
8. Try keyb.com from FreeDOS (http://projects.freedos.net/keyb/).
Look for keyb2.0 pre4 as older and newer versions are known to
have a bug in the loader routines."
Hope that helps.