I have a 1994 Chev. C1500 2wd P/U 5.7 liter V8. Runs fine during daytime when good weather. At night or if there is a change in the weather such as rain, the truck stalls when stopping at a stop sign or stop light, and is very sluggish, acting like it will stall especially going up an incline in the road, the more the incline, the less power the truck has. I have replaced the plugs, wires, distributor cap, rotor, fuel filter, and M.A.P. Sensor. After replacing the M.A.P, Sensor it ran better during daytime, but at night it began the same problems of being sluggish while driving and stalling at stop signs. The check engine light came on and the diagnostic codes indicated the engine is running lean with no other codes indicating any other possible problems. Any ideas or solutions would be appreciated.