1990 Suburban dies intermittently

[SoCalSlaughter]

The vehicle is a 1990 Chevy Suburban V2500 5.7 - TH400. The truck just passed Calif smog, and did pretty well. But its been having a problem recently, doesn't do this all the time. Say if I drive to work, work for 4 hours and go to lunch, on my way home, if I hit a stop light the truck will surge, I will hear a "whistle" type sound and the engine will shut off. It will start right back up and drive. It also does this sometimes when I come to a stop after being on the freeway. Also, if I come to a stop and am sitting for longer then 5 minutes, the truck will surge, I will hear a whistle type sound and the rpms will raise, and it will stay that way until I shut the truck off and turn it back on. Ive already swapped out the IAC, the ECM, distributor, cap&rotor, wires, plugs, tps, coolant temp switch and ICM. Also the truck last year was getting a code 42 (Electronic spark timing circuit open or shorted) But I havent seen the code in more then 5 months. I work next to a speed shop and know the owner pretty well and I have access to many parts. But I just want my truck to run normal. haha Thanks guys