This is not on an f body, but on my dad's 95 fullsize chevy that has a 5.7l 96 vortec motor in it, he used the gmpp manifold to do the swap and other that a few little brackets and extending a few wires everything else was left the same. It ran pretty decent for about 15k miles. Now however it gas fouls plugs, floods itself, and can be started if you unplug the fuel pump relay. Also when it does decide to run correctly when you turn on the cruise control the engine falls on it's face and nearly dies after disengaging cruise it clears back up. It had 02 sensore codes in it, and seemed like it ran better after I replaced it, but now runs like crap again. My initial thought was ect, but it seems to be fine. He replaced it anyways, along with the egr valve, and same situation. Fouls plugs and runs like crap.

Any help would be great, Thanks
B.A.

 

Need a little bit more information about that swap:
ECM used
TBI (injector sizes)
verified fuel pressure readings

Since you have check your CTS, but verify to make sure that you see actual voltage drop across CTS. Check all grounds bad or disconnected CTS ground will cause symptoms that you are describing.
Verify all your sensor grounds and measure actual sensor voltages (TPS, MAP, CTS) while engine is idling.

Bad coil, weak spark is another area you should look into.

//RF

 

Factory ECM (unsure about the p/n)
Factory Injectors, and fuel pressure within factory specs.
That being said I fixed it yesterday, the ects going to the computer, or Fuel injection if you work @ orielly's, had an intermitten connection internally. The plastic on top of the sensor would actually spin a bit from side to side. Resistance measures fine whenthe sensor is just right, but move it a little and there is no continuity.

Thanks for the help,
B.A.