Hey, we are talking about  family here.

HISTORY: 97 Dakota, Ext Cab, 135K, 3.9L, 2WD Automatic.(oil changed
every 3K, without exception)(Rotela).

About 4 months ago I noticed an occasional backfire(no code set).
This progressively became worse, with a noticeable loss of power.
About 2 months ago, it set a misfire code(misfire on #2 cylinder).  I
changed spark plugs, rotor, distributor cap, and spark plug wires.(no
favorable results).  About a month ago it set a misfire code on 2 & 4.
It only sets codes occasionally not every time out.  I have a OBD2
code reader, and the freze frame gives me no clue as to what is wrong.

CONDITION OF THE TRUCK NOW:  Starts good, has a slight lope at
idle(barely noticeable ).  Put your foot on the brake and shift into
Drive or Reverse and the lope is very bad.  Driving,it is very weak on
power, and when you floor it(unless passing gear kicks in) it is so
weak it is hard to get into interstate traffic.  And with the throttle
full open it backfires almost every time.

WHAT I HAVE DONE(not mentioned above)  I have, to my satisfaction,
eliminated the following(right or wrong).  No vacuum leak.  Fuel
preasure is OK, Compression test is OK.  Run fuel injector in gasoline
twice.  Back preasure is OK(disconnected exhaust ahead of cat-conv).
With a digital volt meter I have found the following items to be with
in tolerance. Battery Temp, Air Temp, Coolant Temp,  Map sensor, IAC
valve motor, Cam sensor.  The PCV is like new.

DESPERATE MOVE:  I took it to the Dodge Dealership.  After 6 hours in
the waiting room, this is what they told me.  We have went as far as
we can right now, we believe the problemto be mechanical, and we do
not have a Valve cover gasket.  If you like we will make you another
appointment and order the gasket.  I ask about the appointment and
they said it would be 2 1/2 weeks before they could get too it.
Theycharged me a diagnostic fee, and said they would probably have to
replace the rocker arms(they thought they could hear something loose
on one side).

On my way home I stopped by Autozone and bought the valve cover
gaskets.  Removed the Valve Covers and found nothing wrong.  I also
found they had re-gapped my spark plugs to .30 not .40 as shown on the
sticker under the hood.

MAYBE A CLUE:  At an idle, I can unplug the #4 fuel injector, and
there is very little or no change in the engine rpm or sound.  It
sounds as though the IAC valve does not re-lean the mix.

Any thoughts on this matter will be deeply appreciated.  I know the
truck is old and worn out, but so am I.(It's a beauty, when I had the
oil changed the attendant wanted to know if it was an 05).

Best wishes to all: Rogerx