Chevrolet Repair: TBI and Old Gas, time jimmy, tool truck

Question
I recently bought a 1994 Chevy P/U 4.3L that had been setting for 2 years. After having it serviced for fluids and driving it for 3 weeks it started hesitating and almost died on the highway. I limped home opened the air cleaner and found varnish on the TBI assembly. Replaced the Fuel filter and cleaned varnish with spray chem tool. Truck will run at mid to upper RPM's but will not Idle. Any suggestions.

Answer
You said it sat for two years..did you replace the cap and rotor as well when you did the fluid change?  You may have got some corrosion in the cap.  Also check the wiring in the trucks engine compartment.  Make sure a little critter didn't make a home in there and chew some wires.  It did sit for a long time
Jimmy