How about the fuel filter in the carb inlet fitting.

Check vacuum hose and connection on the back of the carb and the
hose connection from there to the bottom of the air filtre pan.
If that's okay then check the hose to the map sensor, usually mounted
on the firewall. Look for cracks in the hoses and remove the hose,
carefully and see if it comes away easily or is connected firmly.
Since you mentioned your exhaust was replaced, did they put smaller
diametre pipe on rather than the large diameter that came from GM?
I doubt that's the problem, but worth checking.
You had the fuel filtre replaced, so was it installed correctly? Or did

they say it was replaced and they didn't do it? I doubt that's the
problem
because a dirty fuel filtre usually causes stalling at idle.
Those carbs need tightening to the manifold occasionally, but don't
over
tighten the bolts or you'll strip them. Get a lenth of hose and with
the engine
running, put one end of the hose to your ear and move the other end
around the
base of the carb to see if you can hear any hissing for vaccum leaks.
Be careful for moving engine parts when you do it.
My two cents anyway . . .