5.7L TBI Stalling/Hunting Park/Neutral

[Elk4one]

This is going to be a long one, please stick me on this and please forgive a Ford guy switching to GM

 

1991 K1500 5.& TBI hunts then stalls when in Park or Neutral once engine gets into closed loop in between 145 - 160 is when it starts. What i mean by stalling is it seems like it is running out of fuel, tach will go from 600-350 to 500 - 350 and then cut out somtimes it will do this for 10 minutes sometimes 20 secs. I can put it in drive all with brake or parking on and it will not stall unless you are driving and slow way down (about 3-5 mph) to make a right turn. With A/C on it does not stall in park or neutral or turning. No codes or check engine light, starts right back up after stalling/shutting off. While driving I have noticed the tach bounces up and down when letting off the throttle, but does not move if keeping constant pressure on throttle only while decelerating does the tach flucuate about 5-800 rpm. 

 

I have changed TPS, Coolant temp switch x2, t-stat, TBI, AIC valve x2, TBI gasket, O2 sensor, injectors, plugs, wires, cap, rotor, ignition cotrol, distributor, EGR, EGR accuator, vacuum lines, CAT, pressure regulator, brake booster (was rusted and needed a new one). 

 

No vacuum leaks, run lpretty good for a 30 yrs old truck w/stock engine, will run 80 down the highway without an issue. 

Gas mileage is horrible talking big block numbers 8-11, cruising at 70 long trip abouy 140 miles avg about 13 through Nebraska.

New/rebuilt transmission less than 1k miles, problem was prior to tranny self destructing. All fluids have been changed

 

Can someone please point ime n a direction I have not already been. What am I missing here? Am i loosng a fuel pump, ECM? wouldn't think so as I can sit in drive and not stall but about 15 secs after switching from drive to park it starts hunting and then stalls out, but truck will restart immediatly and idle for a time then start all over again.  Unpluggin the O2 makes go high idle (righ((normal), unl=plugging TPS kicks check engine light on, Unplugging IAC make engine go stupid, unplugging coolant sensor also kicks it in high idle rich condition.

I am not a novice mechanic, 30 yrs of working heavy equipment (Diesels)

 

I think I covered everything that I have done and what the truck is doing. I am open for suggestions hopefully someone on here has the same issue and figured it out

 

V/r

Elk4one

[greatmizzou]

What electrical checks have you done?

 

Ive got to tear through mine and replace worn battery cables and clean up the grounds.  My fuel gauge needle looks like its on meth and if I slap the dash I can get the speedometer to turn on or off. 
 

I generally will want to make sure the 12V system is happy before replacing anything other then like an obvious leaking water pump or worn belt.  

[richard wysong]

Maybe bad MAP sensor?