3.1 chevy in a 1993 barretta stalls when warmed up.

hi, i bought a 93 baretta that had what i was told was an issue with the car stalling
when warmed up due to a bad intake gasket. i was able to get the car cheap, and had
no issue changing the intake gasket. the car has 96,000 miles and is in great shape,
so i changed the intake gasket, but could not see where on the old one where it may
have failed. after the intake was replaced the car had a rough idle and wanted to stall
out. i removed and cleaned the Idle control sensor and it helped, so i replaced it with a
new one. all seemed to be ok. i drove it back and forth to work for a couple weeks and
everything seemed to be ok. it's only about 4 miles each way for me to get to
work.the problems started when i sold the car to my broth in law. i sold it to him this
past winter. it was a very cold winter here in northeast ohio and he drove the car with
pretty much no issues for a month or so when he called me one day. he had been
driving the car all day running errands. alot of starting and shuttiing the car off. the car
stalled out on him and left him stranded in traffic. he was able to get the car pushed
into a parking lot. the car would start right up, but would stall out as soon as it was put
into drive. he waited for the car to cool down while waiting for me to get there. when i
arrived the car started right up and was running fine, so we decided to see if we could
get the car home. we made it about 5 miles in stop and go traffic and it happened
again. we pulled into another parking lot and agian the same issue. start-up and run as
soon as it was put into drive it would stall. i was told a common problem with these
3.1 was a bad fuel injector. i did a test on all 6 with an ohm meter and two had low
resistance i think it was 12 ohms and the rest were like 12.5. i replaced the two
injectors and still had the same problem. my brother in law has an hour drive to work
on the turnpike. 70 mph speed limit and says the car run beautiful under acceleration
and when crusing down the turnpike, the issue is when he is decelerating to pay the
toll at the toll booth the car stalls and the same issue starts. the car will start then
stall when put into gear. 20 minutes of cool down and your off and running again.
replaced the remaining four fuel injectors, same issue. replaced the ignition module
next no luck same. the next thing to try is a transmissiom shift solenoid. he was told
by an old time mechanic that this was another issue these cars had. the transmission
would stay in drive and not shift back down when decelerating. any help on this would
be greatly appreciated. sorry this is so long, but i thought the detail would be helpful in
diagnosing the problem.