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Huh? Demonstration please, as the -m switch absolutely does display tracebacks when the call fails:
$ python -m timeit -s "raise RuntimeError"
Traceback (most recent call last):
 File "/usr/lib64/python2.7/timeit.py", line 298, in main
 x = t.timeit(number)
 File "/usr/lib64/python2.7/timeit.py", line 194, in timeit
 timing = self.inner(it, self.timer)
 File "<timeit-src>", line 3, in inner
 raise RuntimeError
RuntimeError
The only tracebacks it suppresses are those for ImportError during the search process, which is deliberate:
$ python -m missing
/usr/bin/python: No module named missing
It even avoids suppressing the traceback when the module is found and an import error occurs later:
$ python -m timeit -s "import missing"
Traceback (most recent call last):
 File "/usr/lib64/python2.7/timeit.py", line 298, in main
 x = t.timeit(number)
 File "/usr/lib64/python2.7/timeit.py", line 194, in timeit
 timing = self.inner(it, self.timer)
 File "<timeit-src>", line 3, in inner
 import missing
ImportError: No module named missing