You can buy them at NAPA or similar stores.  They run, for your car,
$100-150.
No guarantee this is the answer, but it is something to remember.

On some cars, the electrical connections to the computers are also known
trouble
areas.  The plugs to the units can be examined, and dielectric grease
(nonconducting
grease) can be applied to the plugs to improve electrical contact (by
limiting corrosion).

Unfortunately, when you buy from a parts store, and install the unit, they
usually wont
accept it for credit.

I'm still leaning toward the sticking TCC solenoid idea.   It may not
become active til the engine is warm.   There should be an electrical
connector on the transmission (transaxle)  for the TCC.  

****A good way to troubleshoot this is to disconnect the TCC connector
and see if the problem goes away.****

If so, the best fix is to have the TCC solenoid (or whatever is broke)
repaired...probably $300+.  Or if you don't mind the possibility of
somewhat reduced transmission life, leave it disconnected....on a 5
mile drive it's not going to matter much, I don't think.        

If you don't have the Haines or Chilton's repair manual for that car,
GET ONE!  Both if you can afford it...about $12-20 each at your local
parts store.   Those will explain more about how the systems work and
make you the informed consumer that you wanna be....NEED to be :)
These books always pay for themselves in time/hassle/$$ saved.

You dont need to learn everything about how a car works, but knowing a
little can make the difference between getting ripped off or not...and
knowing whether the shop actually has a clue or whether they know less
than you do-and will just keep replacing parts at your expense til
they find the problem.

And while you're at the local parts store, ask the counter guys about
it.   Not the 19 year old guy, but the 35 or 40+ guy that has
"permagrease" under his nails.   Maybe they can even show you where
the TCC connector is.  Might want to try a NAPA/Federated/Parts Plus,
etc store rather than Autozone or the local discount chain.   If they
start treating you like a dummy...show 'em this message and a copy of
your original post.    

A "good" local mechanic shop or transmission shop should be able to
troubleshoot this.  Lots of those cars around and  I suspect it's  a
common problem.

Let us know what you find!

--Don
Don Byrer
Radar Tech & Smilin' Commercial Pilot Guy
Amateur Radio KJ5KB
kj5kb-at-hotmail.com

"I have slipped the surly bonds of earth; now if I can just land without bending the gear..."
"Watch out for those doves...<smack-smack-smack-smack...>"

This sounds almost exactly like what used to happen with my old '88
Celebrity which had the 2.8 V6 similar to the Lumina 3.1.

When hot it would often stall out just after letting off the gas, especially
in stop and go traffic.  It was not the problem with the torque converter
failing to unlock, my dad had that happen in his Cutlass 3.3 and that was
much more violent than the problem with the Celebrity.

What seemed to fix the problem was a pretty serious cleaning of the throttle
body and the idle control valve.  I took the intake tube off and used a rag
soaked in throttle body cleaner to clean up around the throttle plate and
sprayed inside the throttle body.  Made a big cloud of black smoke when it
started up afterward, and seemed to fix the stalling.

Hope that helps!