Chevrolet Repair: bad running engine, throttle position sensor, vacuum hoses

Question
I have a 1988 chevy 1500 pickup with a 5.7L engine. My problem is that after the truck sat for 6 monthes it started starting hard and would not hold a smooth idle, (it will die if I dont keep feathering the pedal) also it hesitates badly upon acceleration and will only run smoothly when revved (after a 2 to 3 second hesitation) after which it starts stumbling again at any part throttle position. I have changed the fuel filter, cap, rotor, air filter, both injectors and new gas. The plugs and wires look fine and the only code I would get from the service engine soon light was a 44 (lean exhaust) which quit after I reset the cumputer and changed the injectors yet I still have the same problem. The truck is only driveable after it warms up and even then the same thing occurs though not as bad.(also with very sluggish throttle respose and lack of power) And after a warm restart forget it the truck is almost impossible to keep running.I would appreciate any input you could give me on this because i've about run out of ideas.

Answer
Hello Jerry,
I would look for rodent damage, to vacuum hoses and wires.
Put some injector cleaner in the tank...a couple bottles.
I also would like to test the fuel pressure. It needs to be 13PSI at the throttle body with the engine running. You could have a pressure regulator problem. It is in the throttle body.
Testing the throttle position sensor may also be needed.

Van.