Hydrocarbon emissions are basically unburned raw gasoline molecules. High HC
from the exhaust pipe usually happens when the fuel in a combustion chamber
fails to ignite, and this is referred to as a cylinder miss. Anything that
can cause a miss can cause high HC emissions. The ignition system is usually
the first suspect and an ignition analyzer is probably the best diagnostic
tool for gathering information on that system, but your basic tune up should
cover most of the components that would be involved. If the plugs and  wires
are not new, then you might consider replacing them before spending too much
money on other items. A compression test might be a good easy check to make
sure it is not a basic engine problem and be sure your maintenance has
included servicing the PCV system. Sometimes a vacuum leak can cause a lean
misfire which will increase HC, so be sure to check out all the possible
sources for that. Of course,  the main component that reduces HC emissions
is the catalytic converter and at 104,000 miles you may be having problems
with it. Because you said you feel a miss or roughness though, I would lean
more towards suspecting a combustion chamber event as being the source of
the high HC emissions.  Other than checking the wires, plugs, compression,
and vacuum systems there is always the possibility that some computerized
emission systems are involved and a good tech might be able to analyze the
data stream for clues to the source of the problem.
Not sure any of this info helps much, but at least now you should have a few
things to consider.

Tune-up!!!