Thanks to all who chipped in ideas. Based on what I've gleaned from your ideas in this thread as well as trading several emails with someone in IAR technical support, I've concluded that I'll be trying the following (wish me luck).

1. Create more stack space by doing the following:

A. Switch to placing user "C" function return addresses on the XDATA stack using the -u option.
B. Switch to placing user "C" function passed parameters & local variables on the XDATA stack using the -E option.

2. If I'm still having stack problems, look for ways to minimize stack usage such as:

A. Merge functions as makes sense.
B. Replace functions with macros where it makes sense.
C. Minimize static local variables if they are using internal RAM.

Maybe down the road I'll be able to rework more of this code & get back to a single internal stack again.

Jeff