Car fun (not)

My '95 suburban has been acting rather strange lately. I was experiencing a loss of power during acceleration, and it was stalling at stop signs. So, we have been trying to solve the problem. Now, we're about $400 later, and we've done the following:
-Fixed the THERMAC sensor
-Replaced two Temperature Sensors on the engine
-Tested the TPS (Throttle Position Sensor) (it was fine)
-Replaced the Spark Plugs
-Replaced the Spark Plug Wires
-Replaced the Distributor cap
-Replaced the Rotor
-Replaced the Ignition Module
-Replaced the Ignition Coil
-Replaced the Pickup Coil
-Replaced the MAP (Manifold Air Pressure) Sensor
-Replaced the ECM/ECC (Engine Control Module/Engine Control Computer)
-Replaced the EGR Valve
-Replaced the Oxygen Sensor
-Replaced the IAC (Idle Air Control) Valve
-Built an OBD 1 ALDL Serial cable to diagnose the engine with from scratch
-Checked for Vacuum Leaks (none found so far)

At this point, we've cleared all trouble codes, and seem to have narrowed the problem down to the idle. The car has power again when accelerating. But, when idling, the mixture becomes too rich, and the car stalls (We know this from running the diagnostic software on it, which is really cool). I'm sick with frustration. What do we do now? It's a TBI (Throttle Body Injection) system. The next steps I can think of are to check for vacuum leaks again, maybe disassemble and clean the TBI "carburetor" unit itself, and check the EST (Electronic Spark Timing) wiring for continuity and resistance problems. Any thoughts?