Chevrolet Repair: 1992 chevy 1500 stalling when I come to a stop., chevy 1500, vacuum lines

Question
Truck is a 92 chevy 1500 2wd with 4.3l v6.  Engine starts right up with no problems, but after coming to a stop, the check engine light comes on and the engine idles down until it stalls.  It runs great and shifts good otherwise.  I have replaced the following items, spark plugs, wires, cap, fuel filter, fuel pump, pcv valve, and a couple suspect vacuum lines.  I have checked the egr valve but did not replace it (i did clean it some, though the diaphragm did seem stiff.  Should it be replaced as well, or is this normal?)  I checked the air intake to insure no blockage.  Fuel injectors themselves dont look all that pretty, but the spray is good.  Although when i recently had the stalling issue, i left the vehicle in drive with parking break on and open up the air cleaner assembly to check it.  There was a rather loud hissing/whistling noise coming from throttle body.  After check engine light went out, and idle went back to normal this noise went away.  I have checked and adjusted the timing to vehicle specs and while this decreased the frequency that the problem occurs, it did not stop it altogether.

I tried to be as accurate in the description as possible.  If you need any other information let me know and Ill domy best to help out.  Thank you for your help.

Answer
Hi Brian... this may sound a little odd but could the lock up in the torque converter be stuck on. easy way to check is to unplug the lock up and see if the stall problem goes away.The engine will stall if lock up is engauged... also if egr is stiff you should repace it...hope this helps