88 Iroc with 5.7. This issue has been going since the beginning of last summer. Car runs great but stalls when down shifting and rpm drops suddenly below 1k...this usually occurs when slowing to a red light. fuel pressure is good, fuel pump seems fine. just replaced IAC valve.

Any advice on where to start would be much appreciated...

 

Whens the last time you did a tune up to the motor? It also could be youe tps its a start.

 

check your distributor see if you have any play in it.i had same trouble, i took mine out and it had a bad innner bushing. it messed up the timing causing stalling. take off the cap and grab the rotor see how mush play there is. how many miles on your engine ? hope this helps

 

check your mass air flow sensor! it's often neglected, but even a small amount of contamination will make your car run bad, stall, and get ****ty fuel economy.