Also... I've noted that when a breakpoint is hit (or single step), the stack trace view (typically on the left side of screeen) shows the threads as 1 line, but it is essentially hung. After a few seconds, the threads are expanded to show their call stacks. When that expansion happens, the debugger becomes usable. I think this means that xcode is spending several seconds figuring out the the call stacks for all the processes (about 17 of them for me) and that is slowing things down. FYI...

Thanks for the help! it is quite painful to have a single step take 7 seconds and more to get a variable's value... What do you mean by "restore the dSYM in the Derived Data"? In "Build Options" for my project, I changed "debug information format" set to "DWARF with dSYM file" (it was just "DWARF" before). It then ran a clean on the project, rebuilt it all... and I'm still getting 7 second single steps... Am I doing the right fix?