Michael, this group has amateurs who play with cars in their spare time when
they are not amusing themselves with something else (like me), and very few
high caliber, experienced pros (like Jim Warman). We all deeply appreciate
the latter group contributing their time here for free, when they could be
making oodles of money for themselves or for their employers instead. To
help them help you quickly and efficiently, put yourself in their place.
They can't see or hear your vehicle and don't know its history, so you have
to provide it here. When you have a problem with an engine, you have to say
what engine it is, how it has been maintained, how many miles; and provide
the best description of the problem and what have you done so far to resolve
it, not just a snippet of what your code reader extricated out of the
computer's memory. Makes sense, doesn't it?

My Expy has the 5.0L engine, so I can't contribute anything from my
experience about your 4.0L SOHC. In its early days your engine had a whole
bunch of problems like faulty intake manifold and timing components. If
those have not been taken care of, it's probably a good idea to google the
archives of this group for symptoms and solutions to those. Otherwise there
are no miracles: systematic troubleshooting will get you to the root cause,
and the Power Train Controls/Emissions Diagnostics Manual will provide that
in great detail. With an engine that has already served 200K, I would not
ignore what that manual calls "Base Engine" - mechanical issues related to
the engine itself. Get a good look at the plugs, comparing the one in the
misfiring cylinder to the others. If you don't know how to 'read' plugs,
learn that - the information is available everywhere. A leakdown test is
ideal, but a simple compression test will also point you to a major problem
in that cylinder, like a stuck valve or piston rings that are not sealing.

The code for insufficient EGR flow seems to be an easy target. If that's
consistent, repairing it may address some of the other issues. The most
common cause is a faulty DPFE sensor, but it could be a clogged hose, bad
solenoid, etc, etc. The same manual will guide you through the systematic
diagnostics if you are not a gambler.

Some will question the wisdom of all the time and expense of doing this on
your own -- or even of doing this at all, instead of dumping the 10-year old
vehicle and buying something newer. I don't have a good answer. Except
perhaps that my 22-year old, throttle-body injected LTD still passes
emissions with flying colors (anybody knows a source of replacement window
sweeps?).