1989 Pontiac Firebird engine problems

Ok lets start with this driving at 75 mph car starts to buck and skip check light comes on then of car runs ok again for a few miles then does it again, come to light it stalls, starts up and goes ok, as you slow does again light comes on, check code says 42, ok this is what I have done so far. New cap, rotor, wires, plugs, dist, temp sensor, ecm, coil, vac lines, also change the module 3 times, still does the same as before, noticed when you start it runs great at warm up then it starts, fuel spray is good at start up then one injector spits snd sputters then goes good for a min, then back again, when checking the for code the light for shift comes on and causes the engine lite to go stupid for a min, then is ok still get code 42 any ideas im stumped