I'm at my wits end, and I'm hoping someone here can point the way.

I bought a QuadCab Dakota in 2000.  Haven't had much problem with it,
other than the PCM module having to be replaced in 2002.  Been very
dependable.

But my heater core sprung a leak two winters ago, and I finally got
around to replacing it last fall.  Note that everything was fine, except
for the heater.  So I spend a weekend tearing the whole $*#! truck dash
out to get to the $100 heater core that could have easily been desined
to slip out through the engine compartment.  But I'll leave that rant
for another thread, as I have another whole list of headaches.

When I got everything back together, the ABS and brake lights stayed on
constantly.  I assumed something was unplugged, but I couldn't find any
problems.  Brakes worked, so I drove it.

Now, the engine would die at stoplights.  If I hit the gas as it dropped
through 600RPM, it would keep running with no problem.  If I slowed very
gradually with it in gear, so that it tried to lug up to the stoplight,
it would keep running.  But if I just pushed the clutch in at 1000RPM
and let it drop off, the engine would die every time.  What's more, as I
passed through about 2400RPM, there was a loud 'roar' coming from the
engine compartment that would disappear at around 2800.  To top it all
off, the spedometer wouldn't register speed until I hit about 35MPH.
Further investigation revealed that a small vacuum line coming from that
'dongle' hanging off the front of brake booster to the interior was
pinched.  I had also twisted that 'dongle' while trying to remove the
vacuum line going to the manifold.

"AHA! I found the culprit," I says to myself.  Either the pinched hose
or me twisting the dongle must have broken some sort of diaphram in the
brake booster, which let excess air into the intake manifold, causing an
overlean condition at the stoplight.  This also sucked air through the
broken diaphram at a resonant frequency at 2400RPM, causing the 'roar'.
 Didnt' explain the spedometer problem, but "baby steps", I say.

I spend $100 and an afternoon replacing the brake booster.

The roar is still there, and the engine still dies at stops.  So I turn
to Google and search for a problem.  Turns out there is a problem with a
$30 sensor on the rear end that will cause the spedometer/brake light
problem.  There is also a known problem with the fan clutch that will
cause this roaring problem.  I would go out and buy all the parts
needed, but I find it hard to believe that all these things went bad at
the exact same time.

Can anyone here suggest a set of troubleshooting steps or test that I
can work through to determine if the fan or ABS sender is bad?  Could I
have gotten a bad replacement brake booster?