Need help troubleshooting misfire?

I have a 93 chevy pick up v8 5.7 liter and idles alright in park and neutral but when you put it in gear the idle drops and it stumbles a bit untill it finally stalls all together.no vacuume leaks did a propane enrichment test all over the engine,brand new plugs,cap,wires,and rotor,benchtested the coil and readings come out spec on sec.,and primary,brand new fuel pump and filter,and injectors/the engine is carbeurated but fed by injectors.Also its really hard to time it just perfectly with the light cause the mark keeps jumping all over,im guessing from the misfire.when i first made my marks and used the light it was way off but i think it was because the idle was high so i lined it up as close as i could wich was alot ccloser then where it was and now it backfires when i rev it up even in park.if this was a newer vehicle I would lean towards the cam or crank sensor but being that this cap and rotor im pretty sure that has nothing to do with it or if this motor evn has those sensors.Is there anyone out there familiar with this engine and can tell me if I forgot something down the line or something i missed.and also i have a dtc43. thank you.