200K I'd say you got your moneys worth out of that converter. Definately
can't hurt to replace it.

You '96 should have OBD-II on it.  Have it scanned for fault
codes which may provide a clue especially if it is
misfiring.  Many parts stores will do this free on the
chance you will buy repair parts from them.  If you do this,
write down the exact code and description.  Just because it
may provide a particular code does not mean that part is the
defect.  It must be interpreted along with other symptoms if
any.

As far as check outs to start, use a residue free electrical
cleaner and clean the MAF sensor in the air intake.  You may
be able to get at it thru the intake tube.  If not, it can
be removed with a tamper resistant torx bit.  You can buy a
set of these at many parts store for under $10.  Check
inside your vacuum hose to the fuel pressure regulator for
fuel.  If there is fuel, the regulator is shot causing
excess pressure.  It still may be bad,s o a fuel pressure
check is probably a good idea.  The test guage kit is about
$40.  I am assuming you have kept the plugs, wires, cap and
rotor maintained.  If not, a good basic tuneup is in order.

After you clean the MAF, you should disconnect the battery
for 10-15 minutes to clear the ECM.  Restart the engine
without touching anything.  Let it idle for a few minutes
and then move the selector thru all the positions for a few
seconds each to allow the engine to relearn it's idle.
Drive it around for a few miles to let it relearn it's
operating parameters and see how it does.

A plugged fuel filter or weak pump can cause a loss of power
but, they rarely cause a drastic drop in fuel mileage
because the fuel pressure is reduced resulting in less fuel
delivered.

As far as the converter is concerned, yes, it can cause a
drop in power and fuel mileage.  Usually a plugged converter
will result in an unusual exhaust sound like the engine is
is turning into a vacumm cleaner instead of having a normal
engine exhaust sound.  A good muffler shop can remove the O2
sensor and install a test guage to check for excessive
backpressure.  If you need a converter and intend to keep
the trck for a long while, make sure they install a name
brand converter or the OEM converter.  Walker and Arvin are
OEM suppliers with good products.  The best route is the OEM
if you are not sure of the product.  MAny generic fitzall
converters that use a single unit to replace 2 or 3
converters do not usually last very long if you must pass
emissions inspection as we do here.

Theer are other things to be done before you spend megabucks
on a converter that won't cost much to check out first.

Good luck
Lugnut

A plugged up catalytic converter will cause loss of power, and overheating in warm weather. It will always make the exhaust system very hot.

How many miles since you changed your spark plugs and other ignition
parts?