HELP!!! Truck Problem.

[87gmc]

ok so, i havent been on in a while i have been making serious changes to my truck and engine. Well in case you didnt alreadt know i have had this horrendous problem of my truck wanting to die when i am shifting out of park and into Drive or reverse, and sometime it wants to die when i come to a stoplight. well i have been through it a million times and couldnt find anything wrong. I have changed the iacv, checked egr everyuthing is good. Well on with that. i was told by someone a while ago and saw on a website the the 1987 Distributor were bad and thats was my problem well i check my cap and rotor and didnt notice anything wrong so i didnt replace it. well Last week i ended up getting an MSD ignition setup. And my truck performed outstanding. It no longer would die at stoplights and it got 75% better when shifting out of park but will still die on occasion. So it makes me think the problem was with my distributor. Well enough of the rundown. Yesterday my lights were left on for a while i go out and start my truck starts up fine but can tell by voltmeter bat is low, and then i notice my truck is kinda surging like reving sorta. i figure its just low bat so i run it a while and leave. well im on the hight way and its running like **** like can only go 55MPH. so i stop check it out and everything looks good start it back up and it runs fine for a while but i get back into town where i have to stop and go drive again and it runds like $H!T. so anyone have this probelm im at a loss except replace the Distributor but i dont really want to because thats a 300 dollar part.