1987 GMC S15 engine trouble

Engine problem
1987 GMC S15 V6 Two Wheel Drive Automatic 160000 miles

when you slowly rev the engine it dies down and cuts off had the spark plugs and wires changed new distributer cap, roter button, new injectors, new o2 sencer idle positoining switch, the ecm valve and a few other parts, the engine runs fine at a high rmp if you floor the gas but when you let off it cuts off in the low idle speeds. If you have any sugestions please reply. Could this be in the distributer