I'm guessing this is a large part of the problem. I don't have any QMI modems, so I'm not going to be all that useful in debugging this particular problem... but at this point, I think your problem is the modem and not the rest of the config.
You may want to consider doing the following:
- start a new thread specifically to debug the QMI issue. A new thread will get the right eyes on the problem.
- consider closing this thread as solved since we did indeed fix the issue with your clients not having internet access (this was the masquerading setting)... we know that works, and now your problem is the upstream connection not working at all. (if you want to come back and 'solve' this one later, that's fine, too)
For reference when you feel it is appropriate:
If your problem is solved, please consider marking this topic as [Solved]. See How to mark a topic as [Solved] for a short how-to.